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Author name code: brandt
ADS astronomy entries on 2022-09-14
author:"Brandt, Peter N." AND aff:"Freiburg"
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Title: Do Long-Lived Features Really Exist in the Solar
Photosphere? II. Contrast of Time-Averaged Granulation Images
Authors: Brandt, P. N.; Getling, A. V.
2008SoPh..249..307B Altcode: 2008arXiv0802.0204B; 2008SoPh..tmp...64B
The decrease in the rms contrast of time-averaged images with the
averaging time is compared between four data sets: (1) a series of
solar granulation images recorded at La Palma in 1993, (2) a series
of artificial granulation images obtained in numerical simulations
by Rieutord et al. (Nuovo Cimento25, 523, 2002), (3) a similar
series computed by Steffen and his colleagues (see Wedemeyer et
al. in Astron. Astrophys.44, 1121, 2004), (4) a random field with
some parameters typical of the granulation, constructed by Rast
(Astron. Astrophys.392, L13, 2002). In addition, (5) a sequence of
images was obtained from real granulation images by using a temporal
and spatial shuffling procedure, and the contrast of the average of n
images from this sequence as a function of n is analysed. The series
(1) of real granulation images exhibits a considerably slower contrast
decrease than do both the series (3) of simulated granulation images
and the series (4) of random fields. Starting from some relatively
short averaging times t, the behaviour of the contrast in series (3)
and (4) resembles the t<SUP>−1/2</SUP> statistical law, whereas
the shuffled series (5) obeys the n<SUP>−1/2</SUP> law from n=2
on. Series (2) demonstrates a peculiarly slow decline of contrast,
which could be attributed to particular properties of the boundary
conditions used in the simulations. Comparisons between the analysed
contrast-variation laws indicate quite definitely that the brightness
field of solar granulation contains a long-lived component, which could
be associated with locally persistent dark intergranular holes and/or
with the presence of quasi-regular structures. The suggestion that the
random field (4) successfully reproduces the contrast-variation law
for the real granulation (Rast in Astron. Astrophys.392, L13, 2002)
can be dismissed.
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Title: Dynamics of solar mesogranulation
Authors: Leitzinger, M.; Brandt, P. N.; Hanslmeier, A.; Pötzi, W.;
Hirzberger, J.
2005A&A...444..245L Altcode:
Using a 45.5-h time series of photospheric flow fields generated
from a set of high-resolution continuum images (SOHO/MDI) we analyze
the dynamics of solar mesogranule features. The series was prepared
applying a local correlation tracking algorithm with a 4.8´´ FWHM
window. By computing 1-h running means in time steps of 10 min we
generate 267 averaged divergence maps that are segmented to obtain
binary maps. A tracking algorithm determines lifetimes and barycenter
coordinates of regions of positive divergence defined as mesogranules
(MGs). If we analyze features of lifetimes ≥1 h and of areas ≥5
Mm{<SUP>2</SUP> we find a mean drift velocity of 304 m s<SUP>-1</SUP>
(with ± 1σ variation of 180 m s<SUP>-1</SUP>), a mean travel distance
of 2.5 ± 1.8 Mm, a mean lifetime of 2.6 ± 1.8 h, and a 1/e decay time
of 1.6 h for a total of 2022 MGs. The advective motion of MGs within
supergranules is seen for 50 to 70% of the long-lived (≥4 h) MGs while
the short-lived ones move irregularly. If only the long-lived MGs are
further analyzed the drift velocities reduce to 207 m s<SUP>-1</SUP>
and the travel distances increase to 4.1 Mm on average, which is an
appreciable fraction of the supergranular radius. The results are
largely independent of the divergence segmentation level.
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Title: Solar Site Survey for the Advanced Technology Solar
Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
2005PASP..117.1296S Altcode: 2005astro.ph..8690S
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than 2 years of data gathering and analysis. Six
locations, including lake, island, and continental sites, were
thoroughly probed for image quality and sky brightness. The present
paper describes the analysis methodology employed to determine the
height stratification of the atmospheric turbulence. This information
is crucial, because daytime seeing is often very different between the
actual telescope aperture (~30 m) and the ground. Two independent
inversion codes have been developed to simultaneously analyze
data from a scintillometer array and a solar differential image
monitor. We show here the results of applying them to a sample subset
of data from 2003 May that was used for testing. Both codes retrieve a
similar seeing stratification through the height range of interest. A
quantitative comparison between our analysis procedure and actual in
situ measurements confirms the validity of the inversions. The sample
data presented in this paper reveal a qualitatively different behavior
for the lake sites (dominated by high-altitude seeing) and the rest
(dominated by near-ground turbulence).
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Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
2005AGUSMSP34A..04H Altcode:
The Advanced Technology Solar Telescope (ATST) will be the world's
largest aperture solar telescope, and is being designed for high
resolution, IR, and coronal research. It must be located at a site that
maximizes the scientific return of this substantial investment. We
present the instrumentation, analysis and results of the ATST site
survey. Two instrumentation sets were deployed at each of six sites to
measure seeing as a function of height, and sky brightness as a function
of wavelength and off-limb position. Analysis software was developed
to estimate the structure function Cn2 as a function of height near
the ground, and the results were verified by comparison with in-situ
measurements. Additional software was developed to estimate the sky
brightness. The statistics of the conditions at the sites were corrected
for observing habits and the annualized hours of specific observing
conditions were estimated. These results were used to identify three
excellent sites suitable to host the ATST: Haleakala, Big Bear and La
Palma. Among them, Haleakala is proposed as the optimal location of
the ATST, La Palma and Big Bear being viable alternative sites.
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Title: The first decades of JOSO -- the Joint Organization for
Solar Observations
Authors: Brandt, Peter N.; Mattig, Wolfgang
2005AcHA...25..240B Altcode:
In 1969 a group of leading European solar physicists established
the Joint Organization for Solar Observations (JOSO) with the aim to
promote international cooperation and to find an outstanding site for a
new European solar observatory. After an extensive site test finally in
1979 they found excellent sites on the Canary Islands for the deployment
of several national instruments in the framework of the newly founded
Instituto de Astrofísica de Canarias. The well co-ordinated thriving
international cooperation made the continuation of JOSO desirable
even after the fulfilment of the originally planned goals. New fields
of cooperation were found, in particular the ground-based support of
the SOHO mission. After the fall of the “iron curtain” in 1989
intensive collaboration with the Eastern-European institutes was
initiated, and JOSO turned into an enterprise for broad scientific
and technological exchange.
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Title: Families of fragmenting granules and their relation to meso-
and supergranular flow fields
Authors: Roudier, Th.; Lignières, F.; Rieutord, M.; Brandt, P. N.;
Malherbe, J. M.
2003A&A...409..299R Altcode:
3D analysis (x,y,t) of the granular intensity field (11-hour time
sequence from the Swedish Vacuum Solar Telescope on La Palma, Canary
Islands), demonstrates that a significant fraction of the granules in
the photosphere are organized in the form of “Trees of Fragmenting
Granules" (TFGs). A TFG consists of a family of repeatedly splitting
granules, originating from a single granule at its beginning. A striking
result is that TFGs can live much longer (up to 8 h) than individual
granules (10 min). We find that 62% of the area covered by granules
belongs to TFGs of a lifetime >1.5 h. When averaged in time, such
long-lived TFGs correspond to coherent diverging flows which may be
identified as mesogranules. We also find a correlation between the
network and the spatial distribution of TFGs.
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Title: Deriving effective sunspot temperatures from SOHO/VIRGO
irradiance measurements. A starspot modelling approach
Authors: Eker, Z.; Brandt, P. N.; Hanslmeier, A.; Otruba, W.;
Wehrli, C.
2003A&A...404.1107E Altcode:
A method is developed to obtain mean effective sunspot temperatures
from satellite irradiance deficits. Using a formalism derived from
a star spot modelling approach, this method only requires accurate
positions and areas of sunspots - but not intensities. The method
is applied to SOHO/VIRGO spectral solar irradiance (SSI) at 402,
500, and 862 nm as well as total solar irradiance (TSI) measured
during the period 16 July to 17 August 1996, the disk passage of
active region NOAA 7981. MDI full disk white-light images are used
to extract sunspot positions and areas. First, using the spot pixels,
which are identified on MDI images as I<SUB>s</SUB> < 0.92, we find
the mean effective temperature of NOAA 7981 to be =~ 300 K less than
the local photospheric temperature. Because the area is dominated by
penumbral pixels, the temperature is close to a value representing the
penumbra. Second, separating umbral and penumbral pixels, we obtain a
temperature difference of =~ 850 K for the umbra and of =~ 200 K for the
penumbra. Finally, if a 5% binning of the spot intensities is applied,
a temperature deficit of =~ 1000 K is found for the darkest regions
of the spot. <P />Appendixes A, B are only available in electronic
form at http://www.edpsciences.org
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Title: Recurrence of fragmenting granules and their relation to meso-
and supergranular flow fields
Authors: Roudier, Th.; Lignières, F.; Rieutord, M.; Brandt, P. N.;
Malherbe, J. -M.
2003EAS.....9..371R Altcode:
The 3D analysis (x, y, t) of the granulation intensity field (11-hour
time sequence from Swedish Vacuum Solar Telescope on La Palma, Canary
Islands), demonstrated that the granules in the phostosphere are
organized in “Trees of Fragmenting Granules" (TFGs). A TFG consists of
a family of repeatedly splitting granules, issued from one granule at
its beginning. A striking result is that TFGs can live much longer (up
to 8h10) than individual granules (10 mn). When averaged in time, such
long-lived TFGs can be identified to the mesogranules. We also found
a correlation between the network and the spatial distribution of TFGs.
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Title: Evolution and motions of small-scale photospheric structures
near a large solar pore
Authors: Dorotovič, I.; Sobotka, M.; Brandt, P. N.; Simon, G. W.
2002A&A...387..665D Altcode:
The analysis of an 11-hour series of high resolution white light
observations of a large pore in the sunspot group NOAA 7519, observed
on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary
Islands, is described. We used a total of 1782 frames, with average
time interval of 22 s. Special attention was paid to the evolution of a
filamentary region attached to the pore, to horizontal motions around
the pore, and to small-scale morphological changes. The filamentary
region was observed to change its structure back and forth between
penumbra-like filaments and elongated granules. A clockwise rotation
of this region around the center of the pore was detected during the
whole observing period. This rotation had angular velocities decreasing
with time from 7.6<SUP>deg</SUP> h<SUP>-1</SUP> to 2.7<SUP>deg</SUP>
h<SUP>-1</SUP>. Motions inside the filamentary region and around the
pore, including penetrations of photospheric granules into the pore,
were studied in detail using local correlation and feature tracking
algorithms. It was found that the observed filamentary region,
although having some typical penumbral features, was different from
a normal penumbra.
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Title: Evolution of Filamentary Structures in and around a Large
Solar Pore
Authors: Simon, G. W.; Dorotovič, I.; Sobotka, M.; Brandt, P. N.
2002AAS...200.3803S Altcode: 2002BAAS...34..698S
We have studied evolution of a filamentary region attached to a pore,
horizontal motions around the pore, and small-scale morphological
changes, using an 11-hour series of 1782 high resolution white-light
images of a large pore in the sunspot group NOAA 7519, acquired on
5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma, Canary
Islands. We find that the structure of the region between the large pore
and an adjacent micropore was not always filamentary, but varied back
and forth in time between a filamentary structure and a granular one. A
clockwise rotation, at times exceeding 7 deg/h, of this filamentary
region around the center of the pore, was observed during the whole
run. Motions of fine structure around and within the pore were studied
in detail using local correlation and feature tracking. We conclude
that the filamentary region, while it had some typical penumbral
characteristics, was different from a normal penumbra. This research has
been funded by the USAF Research Lab, and by Emeritus Research Services.
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Title: Regular structures of the solar photosphere. (Persistence of
the granular field and trenching in the brightness relief)
Authors: Getling, A. V.; Brandt, P. N.
2002A&A...382L...5G Altcode:
The simple procedure of time averaging, when applied to the
photospheric brightness field, reveals quasi-regular structures of
the photospheric and subphotospheric flows. We use an 8-h sub-set of
the series of photospheric images obtained on 5 June 1993 with the
Swedish Vacuum Solar Telescope, La Palma. First, the averaged images
are far from completely smeared and contain a multitude of bright,
granular-sized blotches even if the averaging period is as long as 8
h. This suggests that granules prefer to originate at certain sites,
where they emerge repeatedly, and the granular field demonstrates a
sort of persistence for many hours. Second, the resulting patterns
display relatively regular structures, which can be revealed only if
the averaging period is sufficiently long (the optimum seems to lie
between 2 and 3 h). The averaged brightness relief is “trenched”:
it comprises systems of concentric rings and arcs as well as straight
or slightly wavy lines and systems of parallel strips. The trenching
patterns resemble the so-called target patterns observed in experiments
on Rayleigh-Bénard convection. In addition, the brightness values
at a local averaged-field maximum and at a nearby minimum exhibit a
distinct tendency to vary in antiphase. Thus, a previously unknown
type of self-organization is manifest in the solar atmosphere, and
our findings support the suggestion that granules are associated with
overheated blobs carried by the convective circulation.
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Title: Time-slice diagrams of solar granulation
Authors: Müller, D. A. N.; Steiner, O.; Schlichenmaier, R.; Brandt,
P. N.
2001SoPh..203..211M Altcode:
From a series of 1400 white-light images of solar granulation spanning
a time period of 8.2 hours, skeletal plots of time-slice diagrams are
derived showing intergranular lane positions as a function of time. The
diagrams permit to automatically track, classify, and relate 42 186
granules. Recurrently fragmenting granules are found that survive
by means of their descendants for more than 3 hours. Such long-lived
active granules tend to have a mean spatial distance along the slice
of about 10 Mm. This distance decreases with decreasing minimal
required lifetime. Since active granules are expected to generate a
steadily divergent flow over a long period of time, it is suggested
to identify them as a source of the mesogranular flow. Deficiencies
of the time-slice analysis are discussed. The relative frequency of
different types of granules and the granule decay time as derived
from the time-slice diagrams are compared with corresponding results
of previous works.
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Title: Modeling VIRGO Spectral and Bolometric Irradiances with
MDI Data
Authors: Steinegger, M.; Hanslmeier, A.; Otruba, W.; Brandt, P. N.;
Eker, Z.; Wehrli, C.; Finsterle, W.
2001ASSL..259..283S Altcode: 2001dysu.conf..283S
The last solar activity minimum in 1996 was characterized by
several periods without any sunspots or faculae visible on the solar
disk. Between these extremely quiet intervals, from time to time
a single active region emerged and developed. The passage of these
individual active regions across the visible solar hemisphere was
accompanied by a pronounced variation in the solar irradiance as
observed by VIRGO onboard SOHO. Making use of photometric full-disk
observations of the Sun obtained by MDI we try to reconstruct the
temporal behaviour of the three spectral and the total irradiance
channels measured by VIRGO by applying starspot modeling techniques. In
this paper we mainly discuss possible error sources.
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Title: Computational Methods concerning the Solar Granulation
Authors: Pötzi, W.; Hanslmeier, A.; Brandt, P. N.
2001ASSL..259..223P Altcode: 2001dysu.conf..223P
In this paper an overview is given concerning the automatic detection
of granules in long time series and the derivation of characteristic
parameters.
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Title: Preliminary study of the evolution of solar magnetic structures
and photospheric horizontal velocity fields
Authors: UeNo, S.; Kitai, R.; Ichimoto, K.; Sakurai, T.; Soltau, D.;
Brandt, P. N.
2001AdSpR..26.1793U Altcode:
In October 1997, we made a coordinated observation of the solar
photosphere and chromosphere at Hida observatory (Kyoto university,
Japan) and at Teide observatory (Tenerife) over a 10 day. We obtained
imaging data series continuously during 6 hr 45 min in G-band (4308 Å)
observed with the Domeless Solar Telescope (DST) at Hida on 24th October
(effective FOV; 96″×99″). Additionally, in this observation,
we simultaneously observed image series of the chromosphere during
the latter 4 hr 10 min in H α line center and H α ±0.6 Å. From
these data set, we could detect that emerging flux tubes crossed
the photosphere to the chromosphere and that 'convective collapse'
phenomena appeared at the stage of the spot formation. Moreover,
we confirmed that the lifetime of mesogranulation was about 4000 sec
(70 min) from the temporal evolution of velocity patterns. We show
here only a summary of these observations.
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Title: Coordinated MDI/TRACE/SVST Observations of Sunspots
Authors: Bush, R. I.; Shine, R. A.; Brandt, P.; Sobotka, M.;
Scharmer, G.
2000SPD....31.0122B Altcode: 2000BAAS...32R.804B
During the first two weeks of June 1999, coordinated observations
of sunspots were made by the MDI instrument on the SOHO spacecraft,
the TRACE satellite and the Swedish Vacuum Solar Tower (SVST) at La
Palma. The MDI instrument was operating in a "high resolution" mode
and was obtaining 1.2 arc-second resolution magnetograms and 2.4
arc-second resolution dopplergrams at a one minute cadence. TRACE
observations were made in Fe IX/X 171 Angstroms and/or Fe XII 195
Angstroms together with the 1600 Angstroms and continuum bands at a
1.0 arc-second resolution. The SVST data consist of filtergrams taken
with three 2Kx2K CCD cameras with about 0.4 arc-second resolution
operating in frame selection mode. The first camera used a fixed G
band (4305 Angstroms) filter, the second a fixed blue continuum filter
(4507 Angstroms), and the third a narrow band tunable filter which was
cycled through several positions in the Hα line and the 6302 Angstroms
Fe ~I line. The goal of this investigation is to detail the evolution
of stable sunspots in order to understand the detailed correlation of
photospheric flows and magnetic features. The high time and spatial
resolution of these measurements provides a unique opportunity to
explore the interactions of plasma and magnetic field at the solar
surface. This work was supported by NASA grant NAG5-3077 at Stanford
and NASA contract NAS5-38099 at Lockheed Martin.
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Title: Small-scale topology of solar atmosphere dynamics. IV. On
the relation of photospheric oscillations to meso-scale flows
Authors: Hoekzema, Nick M.; Brandt, Peter N.
2000A&A...353..389H Altcode:
We use a high quality five-hour sequence of images of the solar
photosphere taken at the Swedish Solar Vacuum Telescope, La Palma,
to study the relation of meso-scale divergence with the amplitudes of
photospheric intensity oscillations. Meso-scale flows are determined by
local correlation tracking of the granulation. Statistical evaluation
of the co-location probability of regions with more than twice the
average oscillation amplitude and regions with high or low meso-scale
divergence shows that high amplitude regions are preferentially located
in regions of negative divergence (convergence) and avoid meso-divergent
regions. Additionally we confirm the increase of granule brightness
in regions of positive divergence with the opposite effect in regions
of convergence.
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Title: Fine structure in sunspots. III. Penumbral grains
Authors: Sobotka, M.; Brandt, P. N.; Simon, G. W.
1999A&A...348..621S Altcode:
The properties of penumbral grains (PGs) in a medium-size sunspot are
studied from a 4.5 hour observation series acquired on 5 June 1993 at
the Swedish Vacuum Solar Telescope, La Palma. The application of an
image segmentation procedure and a feature tracking algorithm on a movie
of 360 frames yields proper motions, intensities, and lifetimes for a
set of 469 PGs. Almost 3/4 of the PGs move toward the umbra and more
than 1/4 toward the photosphere. There appears to be a dividing line
(DL) in the penumbra, approximately 0.7 of the distance from the umbra
to the photosphere, such that most PGs outside this line move toward
the photosphere, and those inside move toward the umbra. For inward
moving PGs we find a typical proper motion speed of 0.4 km s(-1) and
a median lifetime of 29 minutes, for outward moving ones 0.5 km s(-1)
and 22 minutes. The average speed of inward moving PGs increases with
distance from the umbra with a maximum near the DL. Outward moving
PGs have maximum speed near the outer penumbral boundary. The measured
instantaneous velocities of individual PGs show only partial agreement
with theoretical model predictions. We find much shorter lifetimes than
earlier authors, and no pronounced dependence of lifetime on position
in the penumbra. We discuss possible reasons for the disagreement with
previous results.
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Title: Shift-and-add reconstruction of solar granulation images
Authors: Baba, N.; Miura, N.; Sakurai, T.; Ichimoto, K.; Soltau, D.;
Brandt, P.
1999SoPh..188...41B Altcode:
To restore an atmospherically degraded image of solar granulation the
shift-and-add (SAA) method is applied to its specklegrams. It is the
first time, to the best of our knowledge, that such a technique has
been used for image reconstruction of solar granulation, a largely
extended target. SAA, therefore, enables us to monitor restored images
of solar granulation in a simple and fast way.
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Title: Resolution Improvement of Solar Images
Authors: Miura, Noriaki; Baba, Naoshi; Sakurai, Takashi; Ichimoto,
Kiyoshi; Soltau, Dirk; Brandt, Peter
1999SoPh..187..347M Altcode:
A method for the improvement of resolution in an observed solar image
is proposed. A blind deconvolution method is used for restoration of an
atmospherically-degraded solar image, and a super-resolution method is
applied to its restored image to improve the resolution. It is confirmed
that a blind deconvolution process can restore fine structures that are
blurred in an observed image, and that the super-resolution process
can make a cutoff frequency in a blind-deconvolved image higher. A
time series of super-resolved images of a sunspot observed with the
70-cm Vacuum Tower Telescope at Teide Observatory is presented.
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Title: Modelling of Solar Irradiance Variations
Authors: Otruba, W.; Brandt, P. N.; Eker, Z.; Hanslmeier, A.;
Steinegger, M.
1999ASSL..239..213O Altcode: 1999msa..proc..213O
A modelling of the sunspot deficit in solar irradiance measurements
in 3 spectral wavelengths and the total flux as observed by the VIRGO
experiment on SOHO has been performed for several periods of 1996 in
a pixel-by-pixel manner using high resolution photoheliograms taken at
Kanzelhöhe Observatory. The calculation of the irradiance contributions
of the other features of active regions is in progress.
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Title: Some Properties of the Solar Granulation and Mesogranulation
Authors: Mühlmann, W.; Hanslmeier, A.; Brandt, P. N.
1999ASSL..239..223M Altcode: 1999msa..proc..223M
Based on a 8.7 hour time series of solar granulation images (Simon
et al., 1994), of a spatial resolution mostly better than 400 km, we
calculated some properties of granules, vorticity and divergence of
the velocity fields and we tried to determine the mesogranular pattern
by corks.
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Title: Small-scale topology of solar atmosphere
dynamics. III. Granular persistence and photospheric wave amplitudes
Authors: Hoekzema, N. M.; Brandt, P. N.; Rutten, R. J.
1998A&A...333..322H Altcode:
We use a superb five-hour sequence of 900 solar images taken at La
Palma to study long-duration persistence in the solar granulation,
in the context of the long-lived “intergranular holes” discovered by
\cite*{Roudier+others1997} %T AA: intergranular plumes + BP formation
and the contention that these mark sites of convective downflow
plumes. We develop a procedure to locate “persistency regions” that
contain granular brightness maxima or minima over extended periods
(up to 45 min), while allowing for lateral drifts due to horizontal
flows. Statistical evaluation of the co-location probability for
different pixel classes is first used to quantify the likelihood of
long-term stationarity for different granular brightness classes and for
the persistency regions, and then to evaluate the amount of preferential
alignment, at different frequencies and time delays, between excessive
Fourier modulation and granular brightness and persistence. The results
support the existence of long-lived intergranular holes. There is large
persistency difference between the brightest and the darkest features;
some of the latter have location memories as long as two hours. In
addition, the darkest intergranular features are found to be sites of
enhanced Fourier modulation in the 3-min acoustic regime, improving
earlier results through much higher statistical significance. However,
the persistency regions containing intergranular holes do not seem
to produce the excess acoustic emission that would be expected above
downflow plumes.
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Title: On the Determination of the Quiet-Sun Center-to-Limb Variation
in CA II K Spectroheliograms
Authors: Brandt, Peter N.; Steinegger, Michael
1998SoPh..177..287B Altcode:
We present a method for the determination of the center-to-limb
variation (CLV) for Caii K spectroheliograms. It is based on the
calculation of intensity histograms for rings of constant area. Using
a simple cutoff criterion in the cumulative histograms, we are able
to derive CLVs of the quiet Sun regardless of the solar activity
level. Using an example from the literature, we show in which way
different methods of normalization of the quiet-Sun CLV may affect
the results.
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Title: Small-scale topology of solar atmosphere dynamics. I. Wave
sources and wave diffraction
Authors: Hoekzema, N. M.; Rutten, R. J.; Brandt, P. N.; Shine, R. A.
1998A&A...329..276H Altcode:
We study the small-scale topology of dynamical phenomena in the
quiet-sun internetwork atmosphere, using short-duration Fourier analysis
of high-resolution filtergram sequences to obtain statistical estimates
for the co-location probability of different fine-structure elements
and wave modes. In this initial paper we concentrate on the topology
of short-duration Fourier amplitude maps for the photosphere and the
simultaneously observed overlying chromosphere. We find that these
maps portray a complex mix of global modes and locally excited waves
which necessitates a statistical approach. Various aspects including
mesoscale patterning indicate the presence of subsurface wave sources
and of subsurface wave diffraction by convective inhomogeneities.
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Title: Fine structure in sunspots. I. Sizes and lifetimes of
umbral dots
Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W.
1997A&A...328..682S Altcode:
The analysis of a 4 1/2 hour series of high resolution white light
observations of the umbra in a medium-size sunspot (NOAA 7519, observed
on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma) is
described. An automatic identification and tracking algorithm was
applied to umbral dots (UDs) observed in a destretched movie of 360
frames. In total, 662 UDs were tracked and their filling factor, sizes,
and lifetimes were measured. It was found that large (diameter >
0farcs 4) and long-lived (lifetime > 10 minutes) UDs appear mostly
in regions with enhanced umbral diffuse background intensity. UDs
do not have a “typical” size. Their number rapidly increases with
decreasing diameter down to the resolution limit. Similarly, UDs do
not have a “typical” lifetime, and their number rapidly increases
with decreasing lifetime. UDs with lifetimes below 10 minutes represent
about 2/3 of the population; the median lifetime is 5.9 minutes.
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Title: Fine structure in sunspots. II. Intensity variations and
proper motions of umbral dots
Authors: Sobotka, Michal; Brandt, Peter N.; Simon, George W.
1997A&A...328..689S Altcode:
Temporal intensity variations of umbral dots (UDs) and dark nuclei
(DNs), and proper motions of UDs, were analyzed in a 4 1/2 hour
time series of high resolution white light images of the umbra in a
medium-size sunspot (NOAA 7519). The observations were made on 5 June
1993 at the Swedish Vacuum Solar Telescope, La Palma. An identification
and tracking algorithm was applied to UDs observed in a destretched
movie of 360 frames. In total, 662 UDs were tracked, and their
intensities, positions, and proper motions were measured. Power
spectra of temporal intensity variations of UDs and DNs were
computed, and several typical periods were found. The histogram of
time-averaged intensities of UDs has two maxima; the UDs belonging to
the brighter part of the population are located mostly at or near the
umbral-penumbral boundary. The number of UDs decreases with increasing
magnitude of the proper motion velocity. Speeds of UDs are grouped
at 100 and 400 m/s. The observed spatial distribution of UDs with
different proper motion velocities is found to be in contradiction to
the generally accepted idea of moving “peripheral” and stationary
“central” UDs. Both “fast” and “slow” UDs are present in all
parts of the umbra. Thus velocity does not appear to be a good criterion
for separating UDs into “peripheral” and “central” ones.
---------------------------------------------------------
Title: On Novel Methods to Determine Areas of Sunspots from
Photoheliograms
Authors: Pettauer, T.; Brandt, P. N.
1997SoPh..175..197P Altcode:
Two novel methods of measuring umbral and penumbral areas of sunspots
and of complex sunspot groups are described. Both methods comprise the
digitization of photoheliograms by a frame grabber and the computation
of intensity histograms of selected areas of activity. The first
method, called `cumulative histogram method', in principle determines
the intensity boundaries umbra-penumbra and penumbra-photosphere
from the intersections of linear fits into the corresponding parts
of the cumulative histograms of sunspots. The second method, called
`maximum gradient method', marks image pixels of a given intensity
level ±2 units wide as a white isophote on a display. Interactive
variation of this level makes it easy to visually select the contour
line fitting the boundary penumbra-photosphere (or umbra-penumbra)
best. At the same level usually the width of the contour line is
smallest. In both cases the summation of the pixel numbers above the
corresponding intensity levels yields the umbral and the total sunspot
areas, respectively. Some limitations of the two methods are discussed.
---------------------------------------------------------
Title: Modelling Solar Irradiance Variations with an Area Dependent
Photometric Sunspot Index
Authors: Brandt, P. N.; Stix, M.; Weinhardt, H.
1994SoPh..152..119B Altcode: 1994IAUCo.143..119B; 1994svs..coll..119B
The He 1083 nm line equivalent width and the 10.7 cm radio flux are
employed to model the total solar irradiance corrected for sunspot
deficit. A new "area dependent photometric sunspot index" (APSI)
based on sunspot photometry by Steinegger et al. (1990) is used to
correct the irradiance data for sunspot deficits. Two periods of time
are investigated: firstly, the 1980-1989 period between the maxima of
solar cycles 21 and 22; this period is covered by ACRIM I irradiance
data. Secondly, the 1978-92 period which includes both maxima; here,
the revised Nimbus-7 ERB data are used.
---------------------------------------------------------
Title: Changes of the Fe I spectral line parameters as a functin of
the magnetic flux (solar disk centre).
Authors: Brandt, P. N.; Gadun, A. S.
1993KFNT....9....8B Altcode: 1993KNFT....9....8B
The parameter variations of the 281 Fe I lines (asymmetry, depth,
equivalent width, halfwidth) are analysed in three regions near the
solar disk centre, having different magnetic fluxes. The analysis
shows that the line parameter variations depend on the line strength,
the lower excitation potential and the line sensitivity to the magnetic
field. A qualitative interpretation of the results is given.
---------------------------------------------------------
Title: Variation of granulation properties on a mesogranular scale
Authors: Brandt, P. N.; Ferguson, S.; Shine, R. A.; Tarbell, T. D.;
Scharmer, G. B.
1991A&A...241..219B Altcode:
A 79 min series of CCD images of the solar granulation with subarcsec
spatial resolution is analyzed. Local correlation techniques are applied
to determine horizontal displacements of the granular intensity pattern
in a 14.2 by 12.2 sq arcsec field of view. The divergence of the average
horizontal flow field shows mean cell sizes of 5 to 7 arcsec. Granules
are selected with respect to area, brightness, lifetime, and expansion
rate. It is shown that small, faint, short-lived, and fast collapsing
granules are located preferentially in the negative divergence
(down-draft) regions of the mesogranular flow field, while bright,
long-lived, and rapidly expanding granules populate preferentially
the positive divergence (up-draft) regions. The differences in area
coverage range between + or - 6 percent and + or - 9 percent.
---------------------------------------------------------
Title: On the Umbra / Penumbra Area Ratio of Sunspots
Authors: Brandt, P. N.; Schmidt, W.; Steinegger, M.
1990SoPh..129..191B Altcode:
The area ratio of umbra to penumbra (A<SUB>u</SUB>/A<SUB>p</SUB>) was
investigated for a series of 126 sunspots observed around the maximum
of solar activity in 1980. Plotting log (A<SUB>u</SUB>) as function of
log (A<SUB>p</SUB>) a linear relation is obtained with a slope of 1.10,
yielding an average ratio A<SUB>u</SUB>/A<SUB>p</SUB> of 0.24 for small
spots and of 0.32 for large spots. This deviates noticeably from the
commonly adopted constant value of A<SUB>u</SUB>/A<SUB>p</SUB> = 0.21
(Allen, 1973) used e.g. for modelling the sunspot irradiance deficit
(cf. Willson et al., 1981) from the Solar Geophysical Data.
---------------------------------------------------------
Title: Sunspot Photometry and the Total Solar Irradiance Deficit
Measured in 1980 BY ACRIM
Authors: Steinegger, M.; Brandt, P. N.; Pap, J.; Schmidt, W.
1990Ap&SS.170..127S Altcode:
Until now a simple Photometric Sunspot Index (PSI) model was used
(e.g. Willsonet al., 1981) to describe the contribution of sunspots
to the solar irradiance deficit measurement by ACRIM. In this work we
replace this model by a photometry of sunspot pictures for the period
of 19 August to 4 September, 1980 taking into account the individual
features, like lightbridges or umbral dots, of each spot. The main
results of this preliminary analysis are: (1) theA <SUB>u</SUB>/A
<SUB>p</SUB> ratios and alsos the α values vary in a wide range and
are by no means constant as in the PSI model; (2) the general trend of
the irradiance deficit from our analysis agrees well with the ACRIM
measurements; (3) on some days there are differences of more than
50% between the deficits derived from our measurements and from the
PSI model.
---------------------------------------------------------
Title: Solar line asymmetries and the magnetic filling factor
Authors: Brandt, P. N.; Solanki, S. K.
1990A&A...231..221B Altcode:
Results are presented of an analysis of high-quality Fourier transform
spectrometer spectra obtained in facular regions near solar disk center
having different amounts of magnetic flux or, equivalently, different
filling factors, alpha. The line parameters (width, equivalent width,
depth, bisector shape, and wavelength) of 32 spectral lines and their
variation with alpha are studied. Line depth is seen to decrease with
increasing filling factor for all the observed lines, while the line
width increases, even after compensation has been made for the Zeeman
broadening. For strong or temperature-insensitive lines the equivalent
width stays practically unchanged, but decreases for weak lines. The
findings are qualitatively explained by a decrease in the contrast
between the upflow and downflow components of the nonmagnetic part
of the atmosphere in active regions (abnormal granulation) coupled to
either a decrease in the average temperature of the nonmagnetic part
or a significant increase in small-scale velocity.
---------------------------------------------------------
Title: Horizontale Eigenbewegungen der solaren Granulation:
Mesogranulation und Wirbelstruktur.
Authors: Brandt, Peter N.
1990S&W....29..164B Altcode:
The main problems related to solar observations are reviewed, and
recent advances in the technology of observation and analysis are
reviewed. Recent findings on the convection dependency of the motion of
solar granules are discussed. These convective cells are 5000-6000 km
in breadth and are called mesogranulation. They are intermediate in size
between those resulting from granulation and from supergranulation. The
observation of an eddy in the mesogranulation is reported.
---------------------------------------------------------
Title: On the fractal dimension of the solar granulation
Authors: Greimel, R.; Brandt, P. N.; Guenther, E.; Mattig, W.
1990VA.....33..413G Altcode:
Fractal dimension analysis may be used to determine whether the solar
granulation represents homogeneous, isotropic turbulence in certain
ranges of scale. Several attempts have been made to investigate
this fractal dimension from white light granulation pictures of
high spatial resolution, e.g. Roudier and Muller (1986), Darvann
and Kusoffsky (1989), and Karpinsky (1990), who find a critical
scale of granule sizes, at which the fractal dimension d changes
abruptly. Using material from the "Spektro-Stratoskop" and analysing 42
742 granules, we could confirm the results published earlier, i.e. a
fractal dimension of approx. 1.3 for the small scales and d ≈ 2 for
the large scales. However, we find a smooth transition between both
regimes. Moreover, a closer inspection of the methods used reveals,
that in all analyses the fractal dimension of the granulation at
small scales seems to be dominated by technical problems, i.e. the
limited resolution of the material, the definition of the granules,
and — last but not least — the finite pixel size.
---------------------------------------------------------
Title: Vortex flow in the solar photosphere
Authors: Brandt, P. N.; Scharmer, G. B.; Ferguson, S.; Shine, R. A.;
Tarbell, T. D.; Title, A. M.
1988Natur.335..238B Altcode:
Convective flow fields in the solar atmosphere play a key role in the
concentration and dispersal of magnetic flux<SUP>1</SUP>, but because
the individual flow elements-the solar granules-are a few arcsec or less
in size, studies of their motions have been limited by the distortion
and blurring of the Earth's atmosphere ('seeing'). We report here a
very high-quality series of granulation images taken at the new Swedish
Solar Observatory on La Palma (Canary Islands) which have permitted
flow measurements at the sub-arcsec level. These movies show a vortex
structure which visibly dominates the motion of the granules in its
neighbourhood and persists for the 1.5 h duration of the movie. If such
vortices are a common feature of the solar convective zone, they may
provide an important mechanism for the heating of stellar chromospheres
and coronae by twisting the footprints of magnetic flux tubes.
---------------------------------------------------------
Title: Day-time seeing statistics at Sacramento Peak Observatory
Authors: Brandt, P. N.; Mauter, H. A.; Smartt, R.
1987A&A...188..163B Altcode:
A method for the photoelectric measurement of angle-of-arrival
fluctuations at the solar limb is described, from which Fried's
seeing parameter r<SUB>0</SUB> can be determined. From a set of
2092 measurements, each of 10 s duration, performed on 146 observing
days in the period from June 84 to September 86 at the solar vacuum
tower telescope of the Sacramento Peak Observatory, a log-normal
distribution of the r<SUB>0</SUB> values gave a median r<SUB>0</SUB>
= 8.7 cm (measured at λ = 510 nm), with a standard deviation σ =
0.25 in logarithmic units. The results are compared with atmospheric
sounding experiment data and longterm day- and night-time seeing
statistics obtained at other observatories.
---------------------------------------------------------
Title: Ändert sich die Struktur der Granulation mit dem solaren
Aktivitätszyklus?
Authors: Brandt, P. N.
1986S&W....25..128B Altcode:
It is pointed out that the 11-year solar activity cycle is of
basic importance for a number of phenomena on the sun itself, in
interplanetary space, and on earth. A number of decades ago, the
possibility was considered that changes in the structure of granulation
are a function of the solar activity cycle. The observational techniques
existing at that time could not provide an unequivocal answer to
this question. In the last few years, the number of observations
which indicate cyclic chanages in the structure of granulation has
increased. The characteristics of granulation are discussed, taking
into account the flow and velocity of matter, changes regarding the
size and appearance of the granules on the sun, the magnetic fields on
the sun, and differences between characteristics in active and quiet
areas. Attention is also given to new information obtained with the
aid of an observational method which is based on an analysis of the
light integrated over the entire visible solar disk.
---------------------------------------------------------
Title: The JOSO site testing campaigns in the Canary Islands
Authors: Brandt, P. N.; Righini, A.
1985VA.....28..437B Altcode:
In 1968 an informal cooperation of European solar research institutions
was established under the name of JOSO (Joint Organization for Solar
Observations). A brief account is given of the site testing carried out
by this organization to find an "ideal" solar observatory site. After
having tested nearly 40 sites in the Mediterranean and Atlantic coastal
areas, it was found that, notwithstanding the great homogeneity of the
maritime airmasses, coastal sites were not suitable for high resolution
solar observations. Consequently, in the search for mountain sites
imbedded in highly homogeneous air, two sites were chosen in the
Canary Islands: Izaña (Tenerife) and Roque de los Muchachos (La
Palma). Aircraft and radiosonde tests of the microthermal vertical
profile in the atmosphere have shown the superior homogeneity of the
Atlantic airmass above the Canary Islands. An extended test of 160
days (in 1979) of meteorological and solar observations performed
simultaneously with two telescopes, both photographically and with
photoelectric seeing monitors, has led to the conclusion that the Izaña
site is somewhat superior to the site at Roque de los Muchachos as
far as daytime seeing is concerned. Measurements during and after the
campaign have also shown that for certain periods during daytime the
telescopes installed at both sites appear to be inside the large-scale
airmass whose residual inhomogeneities limit the night-time seeing.
---------------------------------------------------------
Title: On the centre-to-limb variation and latitude dependence of
the asymmetry and wavelength shift of the solar line λ 5576
Authors: Brandt, P. N.; Schroeter, E. H.
1982SoPh...79....3B Altcode:
Low noise photoelectric measurements of the line profile of the g =
0 Fe line gl 5576.097 combined with determinations of the wavelength
shift of its centre calibrated by use of an I<SUB>2</SUB> absorption
tube are reported. Measurements taken at various limb distances
(1.0 ≤ cos ϑ ≤ 0.2) and along 4 different diameters of the Sun
are used to investigate the behaviour of the line asymmetry (C-shape)
and wavelength shift of the line centre as functions of cos ϑ and of
latitude and to search for possible pole-equator differences.
---------------------------------------------------------
Title: Solar site-testing campaign of JOSO on the Canary Islands
in 1979
Authors: Brandt, P. N.; Woehl, H.
1982A&A...109...77B Altcode:
Results of the campaign of testing undertaken by the European JOSO
(Joint Organization for Solar Observations) in order to find an
excellent site for solar observations are presented. Measurements
with telescopes of 40 and 45 cm aperture and photoelectric
seeing measurements were made at the sites of Izana and Roche
de los Muchachos on the Canary Islands of Tenerife and La Palma,
respectively. Observations obtained on 160 days between April and
November, 1979 demonstrate the superiority of Izana in the area of
image sharpness, although both sites offer an increase of one order
of magnitude in the duration of good seeing compared to existing
European stations. Photographs of the solar granulation taken from
July to November confirm the superiority of Izana, where 4.5% of the
exposures exhibit very high quality compared to 1.4% at Roche de los
Muchachos. Analysis of meteorological records indicates that Izana
is capable of providing 3000 hour/year of usable solar observations,
and suggest an explanation for the higher quality of the Izana site.
---------------------------------------------------------
Title: Solar pulsations and angular coherence of atmospheric
transparency fluctuations.
Authors: Grec, G.; Brandt, P.; Fossat, E.; Duebner, F. L.
1979A&A....77..347G Altcode:
It is noted that radial-velocity measurements in integrated sunlight
are contaminated by atmospheric noise due to inhomogeneous transparency
of earth's atmosphere along the line of sight to the solar disk. A
measurement of the angular autocorrelation function of slow fluctuations
in atmospheric transparency is described. It is shown that the typical
coherence size is about 1 deg and independent of fluctuation amplitudes
of 0.7 percent to 30 percent and that the angular autocorrelation
function provides a link between global transparency variations and
spurious measured velocities. It is concluded that all ground-based
full-disk Doppler measurements should be carefully interpreted because
atmospheric noise is present for periods greater than 5 min and less
than about 90 min.
---------------------------------------------------------
Title: Tests of 4 Single-Stage Image Intensifier Tubes for Solar
Spectroscopy
Authors: Brandt, P. N.; Wiesmeier, A.
1974SoPh...38..517B Altcode:
Atmospheric image degradation can be reduced by shortening the
exposure time. Therefore, four single-stage electrostatically focused
image intensifier tubes with fiber optic output were tested in the
laboratory for their suitability in solar spectroscopy. Under the
premise that the spatial and spectral image scales (Capri: 5.9″
mm<SUP>−1</SUP> and 9 mm Å<SUP>−1</SUP>, resp.) should not be
changed by a premagnification, the RCA tube 8605/V1 in combination
with Copex Pan Rapid film turns out as the best choice. It yields a
resolution of 55 line-pairs mm<SUP>−1</SUP> and a gain of exposure
time by a factor of ≈ 14 over Kodak IV-E in the red, with only little
increase of photometric noise but appreciable pin-cushion distortion.
---------------------------------------------------------
Title: On the Determination of Noise in Photographic Measurements
of Solar Velocities and Magnetic Fields
Authors: Brandt, P. N.; Nesis, A.
1973SoPh...31...75B Altcode:
The noise in photographic measurements of solar velocities and magnetic
fields is assumed to be essentially determined by the granularity
of the film, its gamma, the scanning spot size and the parameters of
the specific spectral line. A formula is derived which serves for a
quantitative estimate of the rms velocity and magnetic field noise when
evaluating spectrograms and spectroheliograms. Four typical examples
are treated and show that the estimate is correct within 20%.
---------------------------------------------------------
Title: Measurement of Solar Image Motion and Blurring
Authors: Brandt, P. N.
1970SoPh...13..243B Altcode:
An investigation being carried out at the Fraunhofer Institut is
described; it has two aims: to establish a simple method for the
quantitative measurement of solar seeing effects and to obtain
informations of their dependence on telescopic aperture.
---------------------------------------------------------
Title: Frequency Spectra of Solar Image Motion
Authors: Brandt, P. N.
1969SoPh....7..187B Altcode:
The frequency analysis of image motion (IM) at the solar limb
was carried out in the frequency range from 0.5 to 50 Hz using a
photoelectric equipment. For a telescopic aperture of 35 cm and
a bandwidth of 0.65 Hz a typical frequency spectrum under average
observing conditions shows a decrease of amplitude from 2 arcsec at 0.5
Hz to 0.4 arcsec at 5 Hz, 0.03 arsec at 50 Hz (and < 0.01 arcsec
at 500 Hz). Visually estimated values of image steadiness seem to be
in better agreement with the r.m.s. value of image motion (scattering
parameter σ) than with the amplitude at a certain frequency (Figures
5a, b). The influence of IM on the quality of photographic pictures
or on spectra of solar fine structures is calculated as a function of
exposure time. Table II gives the IM scattering parameters σ (0.01
arcsec to 4 arcsec) calculated for exposure times from 0.001 to 0.5
sec — valid for a time average. The modulation transfer functions
(MTF, one-dimensional) derived from the IM scattering parameters are
presented in Figure 7 together with the MTF for a diffraction-limited
telescope of 35 cm aperture at λ 6000 Å. Exposure times of less
than approximately 0.01 sec (certain within a factor of 2) render the
influence of IM negligible compared to the MTF of the objective used
for this investigation.
---------------------------------------------------------
Title: Modulation Transfer Functions of some Solar Recording Films
Authors: Brandt, P. N.
1967SoPh....2..211B Altcode:
The modulation-transfer functions (MTF) of four solar recording films
(Eastman-Kodak: 103a-G, IV E, RAR-SO-375; Gevaert: Duplopan-Rapid)
are measured with the aid of an interference device. The MTF is used to
estimate the smallest detectable element of a two-dimensional pattern;
the so-called `detectability threshold' a<SUP>*</SUP> depends on:
intensity modulation m, square of MTF, required signal-to-noise
ratio q, gamma and granularity of the film. The calculated values of
a<SUP>*</SUP> for the four emulsions are given in Table II. Finally
the influence of exposure time on image quality is discussed.