## RT Codes Comparison Project

## 1. Molecular atmosphere Comparison

### • Conditions of the comparison (6SV1, RT3, MODTRAN, & SHARM vs.
Coulson's)

**Table 1.** Conditions of the comparison for a pure molecular atmosphere.

Optical thickness |
τ= 0.1 (λ >= 530 nm) |
τ= 0.25 (λ >= 440 nm) |
τ= 0.5 (λ >= 360 nm) |

Ground reflectance |
ρ= 0.0 |
ρ= 0.25 |
ρ= 0.0 |
ρ= 0.25 |
ρ= 0.0 |
ρ= 0.25 |

SZA |
23.0739 53.1301 78.4630 |
0.0 36.8699 66.4218 |
0.0 36.8699 66.4218 |
23.0739 53.1301 78.4630 |
23.0739 53.1301 78.4630 |
0.0 36.8699 66.4218 |

AZ |
0.0; 90.0; 180 |

VZA |
as in Coulson-s tables (see the Excel file) |

Here SZA denotes the solar zenith angle, VZA is the view zenith angle, and AZ is the
relative azimuth.

The relative differences between the simulations of each code and Coulson's values are
calculated as Coulson-Code|*100%/Coulson.

### • Results of the comparison (6SV1, RT3, MODTRAN, & SHARM vs.
Coulson's)

**Figure 1.** Some results of the comparison with Coulson's tabulated values for a
molecular atmosphere.

Results. An Excel file with VPD results is
available by request.

### • Conditions of the comparison (6SV1 & Monte Carlo)

τ_{mol} = 0.25, ρ_{surf} = {0.0; 0.25}, SZA = {0.0-; 23.0-;
50.0-}, 10^{10} photons.

### • Results of the comparison (6SV1 & Monte Carlo)

**Figure 2.**Results of the comparison of 6SV1 and Monte Carlo or a pure molecular
atmosphere.

Instead of calculating an exact value of TOA reflectance for a given geometric
configuration, Monte Carlo calculates the average value of all TOA reflectances confined within a given
solid angle.

The hemispherical space at the top of atmosphere is divided into a number of solid angles,
specified by VZA and AZ values.

In this case, the angular sampling for the relative AZ space (0- - 180-)
is 22.5-. The sampling for VZA space (0- - 90-) is shown in Figure 2. The boundary VZA values are presented
as angular coordinates. The relative difference varies as the radius coordinate from 0 to 0.4%.