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Data flags in the ASCII data file

The ASCII data files of the SO2 service contain some flags (see the ASCII data file specification): The meaning of the values of these flags is listed below.

 

AMF quality index (AQI)

The AMF quality index (AQI) flags the determination of
  1. data needed by the AMF, such as surface height, surface albedo and geometrical AMF
  2. the actual AMF computation

AQI description allowed range
main flags
-1 no AMF computation wanted
===> only step 'a' mentioned above is performed 		--
0 computation of AMF successful --
initialisation errors
1 No cloud cover information available
===> no match with FRESCO data found, or insufficient data available (this combines with CCI = 4; see below) 		--
2 Error in surface height array indexing --
3 Error in surface albedo array indexing --
error computing geometrical AMF
4 Solar zenith angle out of range
===> should never occur, as the analysis limits the pixels to SZA <= 85 deg 		0. <= solZen < 88.
5 Viewing zenith angle out of range
===> it is unlikely that this will occur 		abs(viewZen) < 40.
error computing cloud radiance weight
6 Error in wavelength 300. <= wavelNm <= 3000.
7 Error in surface pressure 200. <= pSfc <= 1500.
8 Error in cloud-top pressure 10. <= pCld <= 1500.
9 Error in surface albedo 0. <= aSfc <= 1.
10 Error in cloud albedo 0. <= aSfc <= 1.
11 Error in mu0 = cos(solZen) 0. <= mu0 <= 1.
12 Error in mu = cos(abs(viewZen)) 0. <= mu <= 1.
13 Error in relative azimuth angle 0. <= dphi <= 180.
14 Error in cloud fraction 0. <= c <= 1.
15 Error in loop over pressure --
16 Error in radiance weight 0. <= radWeight <= 1.
error computing clear-sky and cloudy SO2 AMF
17 Error in interpolation for clear-sky AMF --
18 Error in interpolation for cloudy AMF --
Notes:
  • Flags 2, 3 and 6 - 16 should in principle not occur; if any of these does occur, something is wrong in the code.
  • Flags 17 and 18 indicate that one of the input parameters of the look-up tables is out of its allowed range.
  • Flags 6 - 18 cannot occur if no AMF computation is wanted (i.e. if only step 'a' is performed).

 

Cloud cover index (CCI)

This flags the cloud cover data used.

CCI description
0 no cloud cover data
1 clear sky mode
===> the cloud-top pressure set to 1013.0 hPa, the value used internally for the sea-level pressure, and the cloud fraction is set to 0.0
2 normal FRESCO mode
3 snow/ice FRESCO mode
===> for the AMF calculation the cloud fraction is set to +1 and the cloud-top pressure is set to the surface pressure; in the output the cloud fraction is set to -1.0
4 missing or invalid FRESCO data
===> if the AMF is calculated, this combines with AQI = 1 (see above)
With FRESCO v5.1 these flags are adapted to also include sunglint: in case of sunglint "10" is added to the flag; for example flag 11 means "snow/ice + sunglint". Since we are not using sunglint, the flag is simply corrected to be 0,..,4.

Two adjustments are made to the FRESCO data without any notification or flagging:

  1. If the cloud fraction is < 0.05, the cloud-top pressure is set to 800.0 hPa, as is done in other applications, and the cloud top height to 2.0 km.
  2. The cloud-top pressure  P_ctop  is made to lie in this range:
          P_min <= P_ctop <= P_surf
    where the surface pressure  P_surf  depends on the coordinates and the minimum pressure  P_min  is given by the AMF look-up table (which currently is 372.42 hPa).
 
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