Minutes of the second Bredbeck workshop
========== FORWARD MODEL WORKSHOP, Bredbeck 19-22 June, 2000 ===========
SB = Stefan Buehler
PE = Patrick Eriksson
JU = Joachim Urban
AE = Axel von Engeln
SB Stefan Buehler IUP
AE Axel von Engeln IUP
PE Patrick Eriksson RSS
DF Dietrich Feist IAP
CJ Carlos Jimenez RSS
YK Yasuko Kasai CRL
UK Ulf Klein IUP
AK Armin Kleinboehl IUP
GK Gerhard Kopp IMK
TK Thomas Kuhn IUP
KK Klaus Kuenzi IUP
UL Ulrich Loehnert MUB
JM Jungang Miao IUP
SO Satoshi Ochiai CRL
UR Uwe Raffalski IRF
PR Peter Rayer TMO
BS Birger Schimpf DLR
FS Franz Schreier DLR
RS Richard Siddans RAL
CT Chikako Takahashi FUJ
AT Ariane Thiele MUB
JU Joachim Urban OBX
CV Carmen Verdes IUP
IW Ingo Wohltmann IUP
Institute of Environmental Physics
University of Bremen / FB 1
p.o. box: 330440; 28334 Bremen; Germany
Dep. Radio and Space Science
Chalmers University of Technology
412 96 Göteborg
Global Environment Division
Communications Research Laboratory
4-2-1 Nukuikitamachi, Koganei, Tokyo 184-8795, Japan
Atmospheric Physics Group
Institute of Applied Physics, University of Bern
Fax: +41-31-631 3765
Institut f. Meteorologie und Klimaforschung
Forschungszentrum Karlsruhe GmbH
D-76021 Karlsruhe Germany
Fax: ++49 7247 824742
Meteorologisches Institut Uni Bonn
Auf dem Huegel 20
Fax ++49 +228 735188
Swedish Institute of Space Physics
981 28 Kiruna Sweden
Fax: +46 980 790 50
The Met. Office
Bracknell, RG12 2SZ
Fax: +44 (0)1344 854026
DLR - Remote Sensing Technology Institute
Fax +49 8153-28-1446
Rutherford Appleton Laboratory,
Chilton OX11 0QX, U.K.
Fax: (44) (0)1235 445848
Fujitu FIP Corporation
Environmental System Business Division
Fax : +81-3-5531-1615
Observatoire de Bordeaux
2 Rue de l'Observatoire
Fax : (++33).(0)184.108.40.206.55
Monday 19.6.2000 PM (Chairman: SB)
o Introduction and aims of the workshop (Chairman: SB, 10 min)
o Discussion of workshop program (Chairman: SB, 10 min)
o Workshop notes and proceedings (Chairman: SB, 5 min)
o Overview of forward models not presented last year (Chairman: PE, 2.5 h)
1) MIRART (FS, 25 min)
MIRART = Modules for IR Atmospheric Radiance and Transmission
Applications: - THOMAS (airborne FIR heterodyne spect. (strat. OH)
- BRUKER high resolution FTS
- PIRAMMYD (limb sounding with Fabry-Perot-Interferometer,
- AERO-X (FTS meas. of jet engine exhausts)
- FOCUS (space borne (ISS) high temp. events)
model: line-by-line (lbl)
catalogs: HITRAN, JPL, HITEMP
line shape functions: Voigt (Humlicek algorithm), Lorentz, VVH*Doppler
continuum: CKD, Liebe, FIRS (empirical)
FOV: pencil, Box, Gauss (for limb, nadir, zenith)
instrument response: sinc, box, Gauss
language: F77 with F90 extensions
math libs: SLATEC Common Math. Lib. (www.netlib.org), BLAS
data format: netCDF interface
flow control: "Namelist"
grid: fine freq. grid at line centers and wider grid in wings
num. quadrature (integration): trapez, overlapping parabolas, spline
intercomparison: in PIRAMHYD study with IROE, RAL, SRON
additional WEB interface is under study
future: - AMiL2DA MIPAS, HGF
- aerosols, scattering
- Voigt optimization, refraction, non-LTE
- code improvement to enlarge spectral range
- conversion to F90 and/or steering with Python
- PE: num. quad. rule for temperature?
FS: explanation of the integration way.
- SB: HITEMP?
FS: HITEMP is HITRAN for higher temperatures: H2O, CO2, CO
- PR: HITRAN recommended for IR?
FS: some wrong O2 isotope data in HITRAN96 in FIR region
but otherwise fine.
2) Karlsruhe (GK, 5 min)
base: ground based
F range: 268-280 GHz
spec. resolution: 1.2 MHz
author: M. Kuntz
cat: HITRAN96, Voigt, VVW line shapes
layers: Curtis-Godson means
sideband filter: sinusoidal
not incl: Dopper broadening, pressure shift, scattering,
inversion: semi-analytical calc. for homog. thin layers
Thikonov-Phillips regularization or optimal estimation
- JU: what is Curtis-Godson means?
- PR: elevation angles possible?
- PE: retrieval with TP regularization how it works?
GK: each constituent has its own regularization parameter
- UL: any climatology needed for retrieval?
GK: we use standard profiles
- JU: any progress in limb sounding?
! GK: no, KOPRA for MIPAS can perform limb sounding
3) MPM89/92 and RTTOV-6 (Peter Rayer, R. Saunders, 15 min)
model: (a) lbl (absorption archive)
water vapor (44 lines), oxygen (30 lines)
and continuum term (O2, N2, H2O)
based on Liebe model MPM89/92
(b) RTTOV-6, fast model for transmittance coeff.
satellites of interest: TRMM , METEOSAT, GOES, NOAA
because of the weather prediction purpose, no
attempt is made to retrieve vmr of trace gases
except H2O and ozone
thermodynamics: LT equilibrium assumed
the model is maintained in the next years for NWP
the code is available since Feb 2000
- CJ: linear terms in the absorption archive accurate enough?
PR: the archive includes also some predictors to minimize errors.
- SB: where is the uncertainty larger lbl or fast model?
in the lbl model except for some channels.
- JU: AMSU-B instrument?
PR: there are 60 GHz oxygen band channels etc.
1013 to 0.1 hPa is the altitude region.
the measurement is the input of the transmittance models
and this output is going into the NWP together with other
information. There is no attempt to do separate retrievals
with this data and model.
- SB: Cirrus clouds?
PR: no information for this because others do this job.
4) MWMOD (UL, AT, 50min)
MicroWave MODel from Simmer (1994)
spec region: 1 to 1000 GHz
dimensions: one dim. model and azimuthally isotropic
scattering: aspherical droplets are implemented from Czekala (1999)
products: TB, scattering, clouds, etc.
MWMOD is separated in three modules:
(a) "ENVGEN": for the setting of the atmospheric and
boundary environment like e.g.:
p,T, humidity profiles
clouds, ice, rain content
wind speed, ocean temperature
(b) "IAPGEN": specifications of FM parameters e.g.:
freq. and FOV, phase function with Lorentz-Mie theory
ocean/ice surface specification
(c) "RADTRA": radiative transfer calculations
with the rad. trans. equation incl. all the
selected topics of the forward model setting
the analysis of clouds and liquid water from profiles is with
this model possible.
MWMOD with non-spherical particles especially for particles
above 1mm size necessary. Cross polarization is remarkably
in this region. T-matrix method is used instead of Lorentz-Mie
theory for spherical particles. See Master Thesis of AT,
Univ. of Bonn, for more and detailed information of modeling and
retrieval of water liquid paths from rain and clouds.
Remarkably is the difference in polarization if one looks from the
space to the ground or from the ground to space.
- JM: way is the polarization difference for nadir and zenith
AT: why this difference exists is not known jet. This is a
subject of the Master Thesis to investigate.
UL: there is a validation campaign this summer to validate
the model with measurements.
- JM: 3. and 4. Stokes parameter can be calculated with MWMOD?
- PR: Liebe MPM9* model can calculate transmittance above 1
caused by adjustments of parameters by Liebe, Hufford
and Rosenkranz. So be carful by using MPM9* models!
- PE: why only positive polarization differences for spherical
UL: perhaps due to assumed T profiles.
- SB: why goes the polarization difference so negative at
120 zenith angle degree?
UL: Czekala assumed special conditions for this calculations.
This is not a general feature.
o Updates of forward models since last year (Chairman: PE, 40 min)
JEM/SMILES (SO and CT, YK, 15 min)
instrument must be shield from electromagnetic interferences from ISS
FOV resolution: 3.8 km
bands: LSB 624.32-625.52, 625.12-626.32
MAES = Millimeter-wave Atmospheric Emission Simulator
for ground based, balloon based and space born platforms
FM1: rad. transfer in the atmosphere
cat: HITRAN/JPL and measurements with Lorentz and Voigt line shape
cont: Liebe MPM89
FOV direction: limb
contributions from antenna side-lob directions to the signal
are possible to calculate
FM2: instrument part
included topics: Doppler shift, beam efficency, calib. loads,
optical loss, standing waves, SSB filter, noise, gain,
freq. conversion, AOS, power to temperature conversion,
IM: inversion model
optimal estimation method, OEM, for retrieval with a priori
- GK: from where are the line broadening parameters?
YK: from HITRAN and own measurements
- PE: non-linearities of the instruments from where?
SO: estimation of 1 per cent non-linearity, mostly from the
- GK: how to treat standing waves in the inversion model?
Moliere-4 (JU, 10 min)
Moliere originally for the Odin instrument developed
special version of Moliere for real data processing, which
is different of the main-stream development of Moliere for
cont: Liebe MPM93, CKD-89
weighting function calculation is done analytically
flow control: ascii input file
differences in the intercomparison with FM of iup-Bremen not yet
Tuesday 20.6.2000 AM (Chairman: PE)
Presentation of ARTS
o General introduction (SB)
- increasing time to change already existing FM is not efficient
- open source software of ARTS for wider development of the model
- present status of the code: not ready for operational data analysis
- code in modern C++ with GNU tools and compiler
- one has to be aware of the memory consumption during the calculations
- to be independent, no existing higher language like idl or matlab
is needed to run ARTS
o Concept of ARTS (SB)
- distinction between workspace variables and workspace methods;
workspace methods have workspace variables and control
parameters as input
- also generic workspace methods can be created
- flow control is performed with an ascii input file which will be
interpreted with the help of the ARTS parser (internal lookup tables)
o Absorption (SB)
- not really finished this work, so only a simplified version
can be demonstrated
- the catalog format is different from other models
- SI units of the catalog entries are used
- flexibility in handling of the records is the aim of the catalog
- tag groups are also implemented. With this one can distinguish
distinct lines of one species for different treatment (e.g. weighting
- the absorption can be calculated per species with the help of the
- every tag group will have its one line list
o Rad. transfer (PE)
- line of sight (LOS) 1D, elevation angle (angle with respect to zenith
direction) and platform altitude are the parameters to define limb LOS
- LOS are divided into equally distant steps or calculations
- T and absorption are linearly interpolated
o Sensor modeling (PE)
- FM is divided into two parts, one for the atmospheric part (FM1)
and one for the sensor part (FM2). FM1 is the input of FM2
- the sensor is treated as matrix multiplications, for each sensor part
a single matrix is build. Nonlinearities are therefore not implemented
- data reduction is also considered (binning, eigenvector decomposition)
- weighting functions (WF) are calculated analytically where possible and
- decomposition of the WF into appropriate parts which are easy to
handle in the calculations (constant part, vertical variations,
changes with changing state vector)
- hydrostatic equilibrium is used for WF of the temperature
- the vertical grid is expressed in pressure not in km.
- because of geometrical reasons, the correspondence of pressure and
altitude is internally used in ARTS for limb sounding
- the spherically symmetric atmosphere which is assumed at the moment
is not severe problem if one would like to include 2D modeling
- at the moment it is not definitely decided where all the different
measurement errors should enter the forward model
o practical demonstration of ARTS (SB)
Presentation of BEAM
o BEAM, Bernese Atmospheric Model (D. Feist)
- general purpose model which is also optimized for fast calculations
for certain conditions with numerical optimization
- the accuracy of the optimized calculations is very good
- spectral line catalog BAMCAT especially developed for BEAM
- the interpolation in the predefined frequency grid is done with
Wednesday 21.6.2000 AM (Chairman: JU)
small group work about the following topics:
a) Spectroscopic matters
(SB, YK, UR, GK)
- with new measurements one can compare data and catalog entries
for crucial parameters
- it should be explicitely stated if the data in a catalog is
calculated or measured
- catalog format as it is stated in the proceedings of the first
Bredbeck workshop is in principal good
- difficulties to merge catalog data into one operational list
for the FM. UL, PE, DF, SB have done this in different ways
for their FM. Perhaps a Japanese groups will do it also for SMILES
- another point is how new information should/will be integrated
into existing structures
- DF has a well worked out algorithm how to merge different
catalogs and to put the information into a flexible structure.
This module will be public in near future
- DF propose that it should be possible to overcome the old
computer capacity restricted format which is now the state.
It should be possible to establish a general data base for
spectral data which will contain every information possible.
The user should then select himself which data set with which
reliability level and which format he will select/take. This
can be done via Internet.
All participants agree and encourage DF to set up such a data
b) Extension to IR
(PE, FS, BS, JU)
it is not a big step to enlarge the freq. range to IR
ground based FTIR
space based limb sounder (MIPAS)
space based nadir sounder (IASI)
other balloon, airborne based instruments
airplane exhaust investigations
- physics problems:
scattering, non-LTE, spec. (CO, CO2).
continua, dry air, H2O: FIR uncertainties.
refraction is also a matter of investigation.
line strengths information is a question (vibrational states).
- computational problem:
narrow freq. grids which leads bulk of frequency based calculations
Therefore an intelligent frequency grid should be used.
Line shape function calculated by decomposition of Lorentz in subfunctions
by Clough and Kneizys in Applied Optics July 1979 is a fast method
D. Edwards, 1991 has proposed another algorithm which is used
MIPAS retrieval uses a microwindow approach for fast calculations
FOV coherent detectors : Gauss
incoherent detectors : box function
- FM code:
+ University of Oxford is writing a detailed FM for MIPAS.
+ KOPRA is a general FM which is used for MIPAS from the the
Univ. of Karlsruhe.
+ It is not really clear if FASCODE is still maintained or not.
In the proceedings a list of references will be given to
different models and intercomparisons.
c) 2D forward model
(RS, AE, CV, CJ, SO, CT)
- RS is presenting the 2D results of the ESTEC MASTER extension study.
Detailed information about this study can be given by RS and
SB. The final report will soon be available (2 months)
(UL, JM, AK, AT)
when the wave length is of the order of the scatterer size the
scattering is of importance.
clouds: 100 micrometer
rain : 500 micrometer
frequency 3 GHz correspondence to 100 mm in wave length
frequency 1000 GHz correspondence to 0.3 mm in wave length
+ for spheres Mie theory is applicable:
Mie parameter is chi = 2 * pi * r / lambda
if chi is smaller than 1, Rayleigh scattering can be used
if chi is larger than 1, Mie scattering can be used
+ for non-spherical particles:
axial symmetry: quasi analytical treatment (T-matrix method)
arbitrary form: volume integration method (DDA)
- radiative transfer:
extension of the simple Beer-Lambert equation for scattering
terms (extinction and source term are different from
- solving methods:
successive order of scattering, Monte Carlo, doubling adding (Evans)
integration into ARTS is difficult because of the different
way of processing the radiative transfer.
e) Application to meteorology/assimilation
(PR, IW, DF, TK)
- frequency band of interest for the ,met. operation
20 to 200 GHz approximately for T, humidity, total column of H2O
- nadir sounding is the normal way
- only LTE is considered
- Operation requirements:
+ fast calculations is the dominant requirement
+ if this can be done lbl calculation is an open question. At
the moment an approximation and pre-calculations are taken into
the FM of transmittance calculations
+ an adjoint FM module will calculate the Jacobian matrix numerically
If an analytic way of calculation is comparable in speed
is not clear.
+ The NWP standard is to divide the FM into
two parts: one which calculates fast the rad. transfer
and one part for fast Jacobian matrix calculation
(best estimate of the atmospheric state vector similar to OEM)
- ground emissivity is still an open question
- additional trace gases which are not included into the FM at
the present can give a systematic effect which can be treated
by including these gases into the FM
- scattering is another matter which should be concerned if
the speed is not going down of the FM
- Future applications:
+ models must cope with the NWP speed and the increasing amount of
data from satellites
+ including trace gases for met. products (e.g. ozone)
+ models have to be comparable with the accuracy of the future
sensors and the improved NWP models.
+ NWP people has to be convinced to take satellite data into
account for their calculations. It is not a priori given that
the NWP people will use this essential input in future.
This is completely different from the atmospheric science
Wednesday, 21.06.2000 PM
Retrieval issues: (Chairman: AE, 2.5 h)
Existing strategies and approaches
o Tikhonov retrieval code (BS, 25 min)
- regularization with quadratic constraints
- additional qualitative information comes from the constraints
of the smoothness of the solution
- numerical stability with generalized singular value
- the determination of the regularization parameter lambda comes
from the L-curve criterion
- current retrieval code is a stand alone package in F90
- in future Python will be used for the scripting language
- ground based FT measurement are processed with this retrieval
- future: additional constraints: profiles larger than zero
automation of simultaneous retrieval of several profiles
comparability of different retrieval methods
application to data of FOCUS, AERO-X, MIPAS, SCIAMMACY, GOME
SB: what is the operator for positiveness constraints
BS: current search in the math. literature for solutions,
but the implementation will be not straightforward
PE: log retrieval for positiveness constraints
BS: with this approach the problem will be then non-linear
which makes it difficult
GK: simultaneous retrieval: how to determine lambda then
BS: relative values from a priori because n-dimensional
L-curve solutions are difficult to find.
Mathematicians will help to solve this
o Neural nets (nn), (CJ, 20 min)
- introduction into neuronal nets and its structures
- the setup of a neuronal net for a retrieval problem is basically
to be found by trial and error. There is no fixed structure
- input: spectra, output: profiles
- advantage of neuronal nets:
is the handling of non-linear problems
computational cost is lower than with OEM
- model calculations performed for Odin
- the retrieval results are very similar for both methods for O3, ClO
- also averaging kernels and errors can be calculated with nn
in the case of nn, the AK oscillate stronger around zero than
OEM. The cause of this is not understood now
AE: how many training sets?
CJ: 500 training sets are used
AE: different nn for different latitude and seasons ranges?
UL: additional information input of the nn?
CJ: not yet but in the future like platform high etc
DF: how is the nn implemented?
CJ: with matlab today but different in future
RS: how is the AK calculated?
CJ: contribution function with nn and afterwards build up with
Jacobian to AK.
JM: what about noise in the nn, will the nn recognize noise?
CJ: it is in principle no general problem
BS: what will be if an actual spectra is out of the training
CJ: there will be of course problems in this case. Therefore
the training set including the FM should be very carefully
o Interfaces between forward model and retrieval algorithm
Urd (PE, 10 min)
- interface to Sculd and retrieval program
- four different variable levels
- correlation functions are modeled Gaussian, exponential or
- Cholesky decomposition method used
PE: be aware of non-linearities in the calculation of the
FS: Python (www.python.org)
- full object oriented free for use scripting language
- the program will be interpreted by the interpreter
- intensive calculations should be done in FORTRAN, C, C++
because of its slow speed
PE: set up of the retrieval with matlab
RS: set up of the retrieval with idl
o Towards the ultimate forward model: (Chairman: SB, 1 h)
Possible discussion topics:
- ARTS should be on a level of a reference model
+ how far can be the approximation ?
- on which level should the scattering implemented?
AMSU-B, MASTER, up-looking mm instruments for H2O column
+ basic scattering model for the first step of implementation:
spherical particles, 3D
+ for what purpose should the scattering included?
cirrus cloud detection/correction, etc.
This determines the complexity of the scattering model
useful levels of scattering model:
. 4 Stokes 3D (full complexity)
. sources for phase functions from Uni Bonn
. MASTER: 2D important, polarization unimportant
. AMSU-B: 2D unimportant, polarization important
- instrumental characteristics implementation
+ no derivatives with respect of instrumental parameters
+ at the moment matlab is used to setup the matrix H (PE)
+ H must be inside ARTS in future
+ it has to be considered that e.g. instrumental modules
are divided into several components (e.g. several AOS in
+ frequency shift should be possible to implement into the
- practical demands:
+ (PR) by calculating the absorption coefficients:
mixing table approach (see GENLN2) for different cases
+ (DF) will the line selection be done?
. cooperation between Uni Berne and Uni Bremen is suggested
for the line data base (DF, SB)
. line selection is to some extend included in ARTS in future
. ARTS should be intelligent to select only the really
necessary lines for the user defined accuracy (JU)
. in BEAM the line selection is automatically done by the
forward model itself, but it is not recommended (DF)
. (SB) suggest that it should be possible in ARTS to write
out the lines which are selected by a single FM run to use
this line catalog in other FM runs as well
. (BS) ARTS should provide some intermediate results for the
+ (DF) which continuum models will be included?
(SB) MPMXX, Rosenkranz, CKD
- atmospheric setup
- surface emissivity
- interpolation (RS RAL uses bi-linear approach for MASTER
Speed / accuracy:
- including scattering should not slow down the FM in
a severe manner
- parallelization of the calculation on a small scale should be
easily possible (e.g. split up in respect of frequencies)
- use parameterized calculations if possible (e.g. lookup tables)
- (DF) reduction in CPU time can be achieved by having a fine
grid at line centers and a wide grid in regions where no spectral
- (FS) the frequency grid is for every altitude level separately
chosen in FASCODE, GENLN2 (valid for FASCODE, for GENLN2 I don´t know
it but I can look it up if necessary). The Voigt line shape
function is necessarily approximated. In FASCODE, the Lorentz
line shape function is decomposed but the sum of the parts
gives at the end the original Lorentz function.
In FASCODE the frequency grid is set up appropriately for each layer
and the transmission/radiance given on a coarse grid (lower altitudes)
is interpolated before combined with transmissions/radiances
given on a fine grid (higher altitudes).
GENLN2 uses a fine mesh (grid) for line center contributions and a
wide mesh for line wings.
FASCODE uses a decomposition of the Lorentz function in fast, medium and
slowly varying subfunctions (with the sum still being a Lorentz)
and accumulates these different contributions line by line.
The contributions are combined AFTER all lines have been calculated
using appropriate interpolation.
- ARTS should not be restricted in the choice of the line shape
function. By investigating influences of the line shape an
approximation will be a severe drawback
- the absorption output will be on a common frequency grid for all
altitudes in ARTS at least at the beginning (PE)
- how to interpolate in general?
+ log interpolation seems superior than linear (DF)
+ there should be a single interpolation scheme for one variable
over the whole interval of interest (PE)
+ atmospheric variables like altitude, temperature, VMR,
absorption linear sufficient in log(pressure) (SB)
+ frequency more sophisticated interpolation schemes make
+ BS suggest that the interpolation schemes should be
hidden in an object oriented (OO) code so that the user
+ (BS) ARTS should provide the information of the interpolation
- distribution can be taken from the Internet
- distribution includes all the code and all the documentation
- a user and a developer version will be available.
The developer version will have a version control
- (DF) at the moment BEAM will work from matlab, idl
+ input/output is given in the matlab environment to
- for retrieval it is needed to perform loops of the FM,
therefore the control file mechanism must support this
- PE has a similar approach for Skuld as DF for BEAM
- with respect to a completely separated retrieval program,
input/output should be as ascii files.
- The FM should provide as much information directly to the
retrieval algorithm as possible
- communication between FM retrieval algorithm is a difficult
task. BS uses python to build the interface of the FM and
the core of the retrieval program
- it is a matter of taste how strong the FM should be linked /
should depend on the retrieval program. It is suggested to
have the FM as independent as possible from specific retrieval
programs (FS, BS, JU).
Minutes Thursday 22.06.2000 AM
o (FS) Web interface at DLR for FASCODE3 (and others)
- the input control file is very hard to understand and manipulate
for users not really familiar with FASCODE
- FASCODE uses many I/O files
- PFUI = Python FASCODE3 User Interface
the interface is written in Python
- introduction page is standard for all applications and
the following pages are dynamically build up for the
- WIMP = Web Interface to MODTRAN using Phyton
- it is planned to have a similar interface for MIRART
- the Python code for PFUI is several thousands of lines long
PE: is it open for all?
FS: in principle yes, but a password is to be given
AE: can different calculations be performed simultaneously?
FS: yes, for every user a unique directory is temporarily created
o Towards the ultimate forward model, cont. (Chairman: PE, 2.5 h)
- partition functions
+ for ARTS SB has asked Bob Gamache for his program "tips".
Documentation will be available soon.
It will be perhaps used as a black box in ARTS.
o Best algorithms for the different parts:
- Presentation: van Vleck & Huber (PR, 15 min)
+ this is the line shape on which Clough et al base the CKD model
+ just for thermal equilibrium (LTE) developed
+ negative frequency expressions can be understood as processes
in negative time direction (going backwards in time to the past)
+ the abs. coeff. satisfies the demand of being an even function of
+ It also fulfills the generalized Nyquist theorem
+ the fluctuation-dissipation theorem is also fulfilled
+ in the microwave region the VVH will reduce to the VVW line
+ in the IR the VVH will be in a form which is also used
by the HITRAN catalog for stating the line intensity
+ PR is writing a book about this topic
PR: the oxygen coupling derived of Rosenkranz is also based on VVH
SB: how to convolute VVH and Doppler line broadening function?
PR: the GENLN2 is also a source for looking how to do the
convolution of the line shape function with the Doppler
line broadening function
IW: where to put the frequency shift?
PR: frequency shift will only be formulated in the line shape
function because the shift is caused by the pressure
broadening so that this is the only proper place to
introduce it in the formulas
PR: MPM93 has played at the line strength and line coupling
parameters to fit the data better. But this leads to
unphysical results if one is looking to the absorption or
transmittance of oxygen. So one has to be careful by using
MPM93 for this particular calculations
PR: eventually the Lorentzian line shape function gives too
much absorption in the far wing of H2O
- Presentation: MAES WF improvement (SO, 15 min)
+ analytical WF of limb sounding with finite antenna pattern:
WF is first calculated for pencil beam antenna and after that
integration of the WFs with the antenna pattern
+ the limb path is divided into five different parts along the LOS
and the WF into three parts which add up together to
the final one
+ estimation of number of steps required to calculate WF for a
typical case: 1.6 10^6
+ this way of calculation has the possibility to reduce the
calculational burden in some simple cases
complicated calculations, use of approximations, hardly to extend
to 2D cases
PE: the thinking for ARTS goes in some details in the same
direction (e.g. "LOS-WF")
- continuum absorption
+ MPMXX are empirically derived so that the frequency range for its
use is limited below 1000 GHz
+ dry air continuum is a point for itself. It is not really clear
from which species and which physics it is coming from in some
aspects. On which level it is really accurate is an open question
+ (SB) Bremen is using Rosenkranz formulation in FM
+ (PE) is it possible to treat all different continuum models
in the same way in the FM?
(SB) not really it is only possible by parameterizing some
models (e.g. CKD) and loosing the original form and with it
+ (SB) it is perhaps the best to write for every model a separate
(PE) then one runs into problems with the different line
catalogs which are assumed in different models
+ (JU) which model is the recommended?
(SB) difficult to say, but Rosenkranz seems to be acceptable
+ (PE) there was an error in the description in MPM92
at a freq. of around 500 GHz with an specific isotopic
O2 line. Fore details ask P. Baron, Observatoire de Bordeaux
+ (PR) there are several typos in the papers of Liebe, so be
+ (PR) in MPM93 the definition of the line strength changed, so is
it compatible with the way ARTS will treat the continuum?
(SB) it will be clearly documented how these things are treated
- surface emissivity
PE: is there a simple model/emissivity values which can be
KK: the emissivity of the ocean surfaces is between .5
(plain surface) and 1 (foam)
PR: S. English has also specific knowledge about this topic
KK: The participants of the specific COST working group also
could give some information
- refractive index (ri)
SB: frequency dependence of the ri should be known for
wide band calculations
PE: influence of the solar light is notable in IR region
for some geometries. CJ has done some work on this
- sparse matrices
PE: TNT is used for ARTS at the moment but it is not so promising
RS: lapack is used at RAL
AK: C++ package DIFPACK used
FS: NETLIB, C++, has also such features www.netlib.org
o Open questions since last workshop (Chairman: SB, 20 min)
Are they solved?
+ ARTS line catalog content and format, solved (Proc. 1. Bredbeck WS)
+ partition functions, solved (TIPS of Bob Gamache)
- radiative transfer:
+ interpolation solved but needs more discussions (linear)
+ transform from LOS grid to retrieval grid, solved (PE, ARTS user
- sensor treatment:
+ H-matrix approach for linear effects, solved but further
discussions needed (PE, ARTS development status)
o Summary (Chairman: SB, 20 min)
- (PE) discussion who is contributing what to the proceedings
+ spectroscopy: YK
+ FM: RS (2d), DF (BEAM), SO (MEAN), FS (IR), PR (met app)
+ scattering: JM
+ retrieval interface: RS, PE
+ retrieval: CJ
+ line shape functions: PR
+ optimization: DF
+ Web interface: FS
+ ARTS: SB, PE
+ layout will be distributed by PE, postscript or PDF format
- Thank you for coming!
minutes written by Thomas Kuhn, iup, 29.06.2000