Image Standardization
(At-Sensor Reflectance and COST Correction)

 

Image standardization is the process of normalizing image pixel values for differences in sun illumination geometry, atmospheric effects and instrument calibration.   Standardizing imagery improves the ability to mosaic adjacent imagery and compare imagery over time (e.g. change detection).  Because some procedures involve collecting in-situ atmospheric measurements and radiometric transfer code (RTC), they are difficult and more costly to implement.   The procedures used by this website are image-based, requiring no additional information other than that provided by the imagery.

 

This website provides three tools that create ERDAS Imagine TM spatial models (.gmd format).   Each tool creates a different .gmd file providing a slightly different approach to standardization.  These tools are designed for Landsat 5 TM and Landsat 7 ETM+ scenes and require, as input, the header file (*.h1) accompanying NLAPS formatted imagery from the USGS at Eros Data Center.

 

1) DN-to-Reflectance Conversion:

This tool creates a spatial model (.gmd file) that converts the image’s digital numbers (DN, or voltage measurements) to at-sensor radiance and computes at-sensor reflectance while normalizing solar elevation angle.  The equation is as follows:

 

Where,

rBandN = Reflectance for Band N

LbandN = Digital Number for Band N

D = Normalized Earth-Sun Distance

EbandN = Solar Irradiance for Band N

 

2) COST Atmospheric Correction:

This tool creates a spatial model (.gmd file) that converts DN to reflectance as in tool # 1, but in addition includes an image-based atmospheric correction procedure using the Chavez (1996) COST method.  The equation is as follows:

 

Where,

rBandN = Reflectance for Band N

LbandN = Digital Number for Band N

HbandN = Digital Number representing Dark Object for Band N

D = Normalized Earth-Sun Distance

EbandN = Solar Irradiance for Band N

t = Atmospheric Transmittance expressed as

 

3) COST without Tau (Dark Object Subtraction) Atmospheric Correction:

This tool creates a spatial model (.gmd file) using the Chavez (1996) COST method, with the exception that it omits Tau (t).  The equation is as follows:

 

Where,

rBandN = Reflectance for Band N

LbandN = Digital Number for Band N

HbandN = Dignal Number representing Dark Object for Band N

D = Normalized Earth-Sun Distance

EbandN = Solar Irradiance for Band N

 

 

Frequently Asked Questions

 

References:

Chavez, P.S. Jr., 1996, Image-based atmospheric corrections—revisited and revised.  Photogrammetric Engineering and Remote Sensing 62(9): 1025-1036.

 

Chengquan Huang, Limin Yang, Collin Homer, Bruce Wylie, James Vogelman and Thomas DeFelice, 2002. At-satellite reflectance:  A first normalization of Landsat 7 ETM+ Images.  WWW URL: http://landcover.usgs.gov/pdf/huang2.pdf, US Dept. of Interior, USGS.

 

Markam, B. L. and Barker. J. L. 1986, Landsat MSS and TM post-calibration dynamic ranges, exoatmospheric reflectances and at-satellite temperatures, EOSAT Landsat Technical Notes, 1: 3-8

 

DISCLAIMER:  The tools on this website are designed for the purposes outlined above.   The RSGIS lab recommends you test the models prior to using them.  The tools on this website are provided “as-is,” without warranty of any kind, express or implied.  The RSGIS lab and Utah State University do not warrant that the operation of the tools shall be error free.  Users bear all risk as to the quality and performance of the tools.

 

Download .exe versions of these tools (password required)

 

If you have questions or comments regarding this website, please contact jlowry@cnr.usu.edu