modis_turbidity - computes turbidity, NDVI, reflectance, optical depth for calibrated MODIS data

modis_turbidity - Computes the water column turbidity index, NDVI, reflectance, and aerosol optical thickness from calibrated, bowtie-corrected MODIS data.

This function requires a TeraScan MODIS license.

SYNOPSIS

modis_turbidity  [ inputfile outputfile ]

modis_turbidity  [ outputfile ... directory ]

Parameter: phase_function.

DESCRIPTION

modis_turbidity computes the following variables for a given input calibrated dataset — assumed to be corrected for the bowtie effect of the sensor — and stores the output in a separate output dataset:

Turbidity index of the water column using 2 calibrated MODIS channels
Reflectance for Channels 13L and 16
Normalized Difference Vegetation Index (NDVI)
Aerosol Optical Depth using marine, rural, continental or 2-term Henyey-Greenstein scattering phase function

Variable	Units	Description
turbidity	none	Index of turbidity
reflect1	radiance^*	channel 13L reflectance
reflect2	radiance	channel 16 reflectance
NDVI	none	Vegetation Index
optical_depth	m^-1	aerosol optical thickness
^radiance = mW/(cm²_steradian_*痠)

PARAMETERS

phase_function

Scattering phase function to be used in computing optical thickness. There are four choices: marine, rural, continent, and hg2. The first three functions are evaluated from pre-computed lookup tables; the last function is a two-term Henyey-Greenstein function, adjusted for current pixel geometry and radiance values.

The default value is marine.

EXAMPLES

scrum% modis_turbidity

in/out files   : char(255) ? t1.00160.1957.bt modis_products
phase_function : char(  9) ? [marine]

REFERENCES

Stumpf RP. Retrospective and future studies of coastal water clarity and sediment loads. Proc. third Conf. Rem. Sensing for Marine and Coastal Env. 1995; 1: 128-139
Stumpf RP and Pennock JR. Remote estimation of the diffuse attenuation coefficient in a moderately turbid estuary. Rem. Sensing Env. 1991; 1: 183-191