ref - Computes the turbidity index, reflectance, ratio of reflectance, and NDVI from NOAA-AVHRR data

ref - Computes the water column turbidity index, reflectance, ratio of reflectance, and NDVI using the 2 calibrated visible channels of NOAA-AVHRR.

SYNOPSIS

ref   [ inputfile outputfile ]
ref   [ outputfile ... directory ]

The single parameter is: output

DESCRIPTION

The function ref calculates the turbidity index of the water column using the 2 calibrated visible channels of NOAA-AVHRR. The function implements the turbidity algorithm of Stumpf (1994) and Stumpf and Pennock (1995). The algorithm initially generates atmospherically corrected water-leaving reflectances for channels 1 and 2 and subsequently uses this information to generate a turbidity image. The algorithm assumes that the radiance due to Rayleigh scattering is relatively uniform over the entire scene.

The ref function derives the following variables and writes them to the output data set:

Variable	Units	Description
turbidity	none	Index of turbidity
reflect1	radiance*	channel 1 reflectance
reflect2	radiance	channel 2 reflectance
Corr_bndratio	none	ratio of channel 1 by 2
NDVI	none	Index of vegetation
^radiance = mW/(cm²_steradian_*µm)

PARAMETERS

output
Specifies the type of data to be output.

Valid options are: turbidity, ref1, ref2, ratio, ndvi

EXAMPLES

npoess% ref n16.01115.1953.avhrr n16.01115.1953.vis
output         : char( 49) ? [ndvi] turbidity ref1 ref2 ratio ndvi

npoess% stats
input file(s)  : char(255) ? n16.01115.1953.vis
include_vars   : char(255) ? []
printout       : char(  3) ? [no]
Statistics  Page 1
 
Count    Good        Mean      Min      Max  Std Dev  Variable
 
710842   710830    1.00852        0     6.24 0.775297  Corr_bndratio  n16.01115.1953.vis
710842   710842   0.148842       -1        1 0.408565  NDVI
710842   710842    10.9097        0   120.08  10.6974  reflect1
710842   710842    20.9209        0   117.25  15.9955  reflect2
710842   710842   -0.100086    -0.45     0.52 0.135497  turbidity

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