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FASCOD3P Use

 
The FASCOD3P model is used to infer clear sky radiance and transmissivity of the atmosphere from the surface to cloud base. Figure 38 illustrates a typical FASCOD3P input file. In this example a bottom-up calculation is performed to determine radiance and transmission to an altitude of 13.8 km.

  
Figure 38: Portion of a typical FASCOD3P `TAPE5' data file. It is used to set various model parameters and input atmospheric temperature and water vapor profiles as a function of altitude.

The input file is comprised of three sub-sections: model calculation parameters, representative altitude levels, and the atmospheric aerological profile determined from radiosonde data at the chosen altitude levels [Anderson ChetwyndAnderson Chetwynd1992]. A $ symbol indicates the beginning of the input file, followed by an 80-character information header. The second row determines various parameters used by the model, summarized in Table 7.    

Parameter Value Definition

HI 1 Use Voight profile

F4 1

CN 1 Default for atmospheric calculations

AE 0 No aerosol calculations

EM 1 Calculate radiance and transmittance

SC 0 Default

FI 0 Default

PL 0 Default

TS 0 Default

AT 1 Atmosphere

MG 0 Default, merge data to output file

LS 0 No laser parameters

MS 0 No multiple scattering

XS 0 No cross-sections

Rows 3 through 6 indicate boundaries: spectral, spatial, and direction of calculation. The first two terms in row 3 are the spectral limits; from 750 to 1250 cm   for this example. The following terms in row 3 relate to the spectral linewidth and strength to use for various cases; each set to .000 to accept the default values. Row 4 sets the boundary temperature and emissivity; 0.000 and 1.000, respectively for space observation from the earth's surface. Table 8 lists the row 5 settings. Row 6 indicates begin (H1) and end (H2) altitudes and slant angle; 0.330 through 13.765 km for a zenith view (.000).    

Value Definition

0 User supplied profile (radiosonde)

2 Path, from H1 to H2 (row 6)

43 Levels in profile, maximum of 64

0 Default, zero absorber if less than 0.1% of total

1 Short printout

7 Default, number of molecular species

1 Write layer data to output file

.000 Default, earth radius = 6371.23 km

.000 Default, altitude of space = 100 km

.000 Default, use mean frequency for refractive geometry 360.000

The next several rows, 7 through 12 in this case, suggest the altitude levels which best represent the radiosonde temperature and moisture profile; where roughly 500 data points are reduced to approximately 50. A 24 character information header, used to infer the number of points and filename of the complete radiosonde data file, separates the altitude level listing from the radiosonde data.

The remaining rows describe the radiosonde data corresponding to each altitude level; where two rows are used for each level. Information is given as follows: altitude (km); pressure (mb); temperature (K); units indicator, AA, for this row; and units indicator, FA33333, for next row. The following line: dewpoint temperature (K), and CO mixing ratio (ppmv). The AA specifies pressure and temperature units. FA33333 implies: F, dewpoint units; A, CO units; and 33333, default to value for model mid-latitude winter atmosphere for the remaining 5 atmospheric species (O, NO, CO, CH, and O ). This is repeated for each altitude. A % symbol indicates end of file. The HITRAN92 atmospheric transmission database is the source for the FASCOD3P transmission data.