==== Summary of email discussion in November ====

I tried to summarize the number of cases and to estimate the CPU time:

=== Surface albedo ===

- 3 albedo values

0.05, 0.1, 0.2 for visible range

0.05, 0.2, 0.5 for O2A band

=== GEO ===

SZA: 20,40,60°, SAA: -90,-45,0,45,90°, VZA: 58.3°, VAA: 196.3°
In total: 3*3*1*5*1=45 combinations

For the test case (~a quarter of the full domain) I required ~30 hours
on one CPU to calculate full high resolution spectra and layer AMF in
visible. Only layer-AMF at 1 wavelength require ~5 hours on one CPU.

=> estimated CPU hours for GEO (full visible spectrum, 500 spectral
points, layer AMF): 45 cases *30 hours * 4 (full domain) = 5400 hours,
with 500 CPUS: 10.8 hours (doable)

As discussed, memory requirements for the data become large with full
spectral resolution, so I suggest to calculate full spectra only for one
reference case (e.g. albedo 0.2, SZA 40°, SAA 0°, VZA 58.3° and VAA
196.3°). Retrieval accuracy can be assessed using layer-AMF.

=>Only layer-AMF at one wavelength require only 1.8 hours on cluster

For O2A-band we still need to investigate, which spectral resolution is
required. As suggested by Huan, it might be sufficient to calculate only
2 wavelengths (absorbing and non-absorbing). We have a good absorption
parameterization which gives the same result as averaged over a
line-by-line simulations (averaged over e.g. 1nm using a box-type
response function). If it turns out that we could use only the 2
wavelengths (or 3?), we would need at maximum 5 hours for O2A band
simulations on the cluster. For full line-by-line spectra (0.005nm
spectral resolution) a lot more (number of spectral points:2000).

=== LEO ===

SZA: 20,40,60°, SAA= 13,353°, VZA=0,20,60°, VAA=109.5, 281.7°
3*3*3*2*2=108 combinations

Computational time will be a factor of about 2.4 higher than for GEO
case, still doable.


=== Next steps ===

1. Run retrieval on test case (visible range, data provided on my
website) and check whether this is ok. Huan, when do you have time for
this? Before I start with more simulations I would like to know whether
everything is correct.

Done. 

2. Decide on cases which require full spectral resolution + layer-AMF or
 only layer-AMF. Is it ok to calculate only for the one reference case
(see above) the full spectrum? I think that we agreed that this is ok.

For all cases full spectra are simulated in the VIS.

3. Investigate and decide on spectral resolution in O2A-band. Huan,
could you define 3 wavelengths which you think would be useful so that
we can test, whether these are sufficient or whether we need full
spectral resolution. Then I would run the test case for the full
spectral resolution and the 3 wavelength bands, respectively.

Simulations for 3 wavelengths bands done, investigation ongoing (see below).


Apart from this:
Run the 1D cloud case for more geometries so that
we better understand the dependence of the results on scattering angle.
This data has been provided.

Done.


==== Retrieval results from Huan ====

[[ftp://ftp-ae.oma.be/pub/from_Yu.Huan/3DCATS/]]