USGS MIPS Reflect Documentation

USGS MIPS Reflect Documentation

This program converts Landsat TM and MSS digital numbers (DN s) to grand reflectance values. The algorithm first converts the DNs to at-satellite radiances by correcting for gain and offset values of the particular spectral band and satellite used to record the data. It then converts these top of the atmosphere at-satellite radiance values to ground reflectance values by correcting for atmospheric scattering or haze, sun elevation angle effect, and multiplicative atmospheric absorption effects. A variable to correct for the multiplicative component is included in the algorithm; for a procedure to select this value see Chavez, 1996. If a multiplictive correction value is not available, the default is no correction(i.e., set value to 1.0).

The equations used are:

    Recorded Digital Number(DN):

      DNi(counts) = GAINi * RADi + OFFSETi

therefore,

    Top of the atmosphere/At-satellite radiance:

      RADi = (DNi-OFFSETi) / GAINi,

spectral band i radiance in units of mWcm-2sr-1um-1.

    Atmospheric Haze/Scattering Radiance values:

      RADi(haze) = (DNi(haze) - OFFSETi) / GAINi,

This should be multiplied by the spectral band width to convert to in band radiance, if desired.

    Grand Reflectance:

      REFi = (PI * D * D * (RADi - RADi(haze))) / (Ei * COS(theta) * THAi),

this is the grand reflectance value for DNi. It represents the percent of reflectance of the incoming energy, therefore, it is a unitless number and the value is always less than 1.

where,

    PI    = 3.14159265

    D     = EARTH - SUN distance, in AUs

    Ei    = Top of the atmosphere mean solar spectral irradiance
            for band i, in mWcm-2um-1

    THETA = Solar zenith angle (90-sun elevation angle in degrees)

    THAi  = Atmospheric absorption coefficient/effect for
            band i; if a value is not available the default
            values are set to 1.  Acceptable values can be
            approximated by using the COS(THETA) or default
            standard values(see Chavez, 1996).

The following information is supplied for the Landsat TM sensors:

The spectral radiances are converted to in band radiance by multiplying by the spectral band width. The values given by Markham and Barker in page III-145 (198?) are:

TM Spectral Radiance (in mW cm-2 sr-1 um-1)*
--------------------------------------------

        TM1     TM2     TM3     TM4     TM5      TM7
        ---     ---     ---     ---     ---      ---
LMIN   -0.15   -0.28   -0.12   -0.15   -0.037   -0.015
LMAX   15.21   29.68   20.43   20.62    2.719    1.438


TM Band Width (in um)
---------------------

          TM1     TM2     TM3     TM4     TM5      TM7
          ---     ---     ---     ---     ---      ---
ISAT = 4  0.066   0.081   0.069   0.129   0.216    0.250
ISAT = 5  0.066   0.082   0.067   0.128   0.217    0.252


ISAT = 4 In-Band Radiance (in mW cm-2 sr-1)
-------------------------------------------


        TM1       TM2       TM3       TM4       TM5        TM7
        ---       ---       ---       ---       ---        ---
LMIN   -0.0099   -0.0227   -0.0083   -0.0194   -0.00799   -0.00375
LMAX    1.004     2.404     1.410     2.660     0.5873     0.3595   


ISAT = 5 In-Band Radiance (in mW cm-2 sr-1)
-------------------------------------------

        TM1       TM2       TM3       TM4       TM5        TM7
        ---       ---       ---       ---       ---        ---
LMIN   -0.0099   -0.0230   -0.0080   -0.0192   -0.00803   -0.00378
LMAX    1.004     2.434     1.369     2.639     0.5900     0.3624

* Notice that if the DN values are converted to radiance values using the GAIN and OFFSET parameters versus the LMIN and LMAX in-band radiance values the same answer is NOT given. This may be due to GAIN and OFFSET values changing and/or the LMIN and LMAX values changing.

Also, the maximum spectral radiances computed using the given gains, offsets, and E values are higher than those given by NASA as the maximum possible. This is because either the gains and offsets or E values are different than the ones they used to determine their maximum radiance values.

Furthermore, the maximum percent reflectance value given for each band by Markham and Barker in the August, 1986 EOSAT technical notes are for no haze and 90 degree sun angle. With sun angles lower than 90 degrees, which always occurs --- usually lower than 60 degrees, the maximum reflectance for each band goes up. Plus, with atmospheric scattering/haze correction the maximum reflectance values are affected.

Files

This program requires as input an unsigned 8-bit image file. It will generate an unsigned 8-bit output image file. The following information is transfered from the input file to the output files(if appropriate):

Image labels
Mosaic labels
Projection labels
History file

Also, the radiance and reflectance values for each DN are written out to the print file . Note that the reflectance values are multiplied by a factor of 100.

Parameters

SENSOR and BAND: These parameters are used to select the satellite sensor and spectral band in which the image was collected. Entering the numbers 1, 2, 3, 4, 5, 6, and 7 for the sensor would represent Landsat TM 4, Landsat TM 5, Landsat MSS 1, Landsat MSS 2, Landsat MSS 3, Landsat MSS 4 and Landsat MSS 5 respectively. There is no default for the satellite sensor, a value must be entered. Band numbers for Landsat TM (sensors 1 and 2) are 1,2,3,4,5 and 7; bands for Landsat MSS are 4,5,6, and 7. The default band is 1.
GAIN, OFFSET, EI and FACTOR: These parameters are used to select the gain and offsets, as well as the solar irradiance and multiplicative scaling factor for a particular spectral band. Default values for both Landsat TM and MSS are available.

Entering zero for the sensor will force the user to enter values for the gain, offset, solar irradiance and multiplicative scaling factor parameters. This allows the user to make corrections to data collected by sensor other than the Landsat TM and MSS systems.
DATE: This parameter is used to select the date in which the image was collected. The date should be entered in the format YYYYMMDD. The parameter is used to calculate the Earth-Sun distance value.
SANGLE: This parameter is the sun elevation angle in degrees.
HAZE: This parameter is the atmospheric scattering or haze value to be used for the given spectral band.