LOWTRAN7 Sun and Moon Models

LOWTRAN7 is an Air Force Research Laboratory (AFRL) atmosphere radiance and transmittance model published August, 1988.

LOWTRAN7 is an Air Force Research Laboratory (AFRL) atmosphere radiance and transmittance model published August, 1988. This project is a translation of the LOWTRAN7 Sun and Moon Models into matlab. It should be noted that LOWTRAN7 has been superceded by MODTRAN and SAMM. For quality Sun and Moon images, AFRL's CBSD models should be used instead. However, it has value as an educational model for K12 and undergraduate work. LOWTRAN 7 is a low-resolution propagation model and computer code for predicting atmospheric transmittance and sky thermal and scattered radiance from 0 to 50,000 cm- 1 at a resolution of 20 cm-1.

In LOWTRAN7, direct or scattered light from either the Sun or the Moon can be calculated. The Sun's irradiance is interpolated from a spectrum, and an orbit correction is applied to compensate for Earth's orbital eccentricity. The Moon's irradiance is calculated using a mathematical model developed and published by Robert E. Turner, et al. (1975) NATURAL AND ARTIFICIAL ILLUMINATION IN OPTICALLY THICK ATMOSPHERES, Environmental Research Institute of Michigan, AD-A021 998, Contract No. DAAA21-74-C-0331. (A pdf of this document is included in this download.) The Moon model applies the spectral geometric albedo, as best as it was known in 1988, a phase factor, and the angular extent of the Moon, to the orbit-corrected solar spectrum. The results are shown in the project image.

The script testSourceFunctions.m exercises all the functions that comprise the Sun and Moon models:

SUN - input the wavenumber, output the exoatmosphere irradiance [W/m2 um]

SUBSOL - compute the subsolar latitude/longitude for day of year and UTC code claims a 1 degree accuracy

DEL - lowtran7 computes the source zenith angle along the line-of-sight for source scattered light, beta is the earth center angle from the observer to the point along the line-of-sight

PSI - calculates the relative azimuth between line-of-sight and observer-Sun-path and the earth center angle between observer lat/lon and subsolar lat/lon

SCTANG - compute the angle between the source rays and the line-of-sight

PSIDEL - compute the earth-center angle between the observer lat/lon and the source lat/lon; compute the relative azimuth between the los and the observer->source path

SOURCE - get solar or lunar exoatmosphere irradiance (sun is factored by the sun-earth distance as determined by the day of year; moon is factored by spectral geometric albedo and phase)

createBlockData_SUNDAT - makes a mat file with populated arrays of the block data that has the exoatmospheric solar spectrum in LOWTRAN7

The solar spectrum, which was a FORTRAN block data, is coded as an array stored in a mat file.
https://qph.fs.quoracdn.net/main-qimg-9f77fdcf3b9d432c49319cf428e3f7c6

The subsolar latitude and longitude are found from very simple equations claimed to be good to 1 degree accuracy:
https://qph.fs.quoracdn.net/main-qimg-d9551a76906145926b15a20b290e5de9

The lunar irradiance phase factor will work for any spherical, exoatmospheric body:
https://qph.fs.quoracdn.net/main-qimg-ac16fe747338e964daa5c284324ef358

The Moon's spectral geometric albedo is as best as they knew it in the late 1980s:
https://qph.fs.quoracdn.net/main-qimg-251a38454666cfb9ba25aac3a8dc90c4