FLAASH Validation
A question that is often asked about ENVI's FLAASH atmospheric correction module is how the algorithm was validated. This help article discussed the validation of the FLAASH algorithm.
FLAASH was developed by Spectral Sciences, Inc., under the sponsorship of the U.S. Air Force Research Laboratory. Spectral Sciences has been an integral part in the development of modern atmospheric radiation transfer models, and has worked extensively on the widely-used MODTRAN atmospheric model since the model's inception in 1989. Exelis Visual Information Solutions has incorporated the FLAASH code into ENVI; we do not develop the FLAASH algorithm.
Exelis VIS does not validate the FLAASH algorithm. We have not calculated any statistics on the accuracy of FLAASH. We simply implement the algorithm as described in the following references, and test to make sure that it is correctly implemented. The Exelis VIS testing consists of running FLAASH on image files provided by Spectral Sciences, Inc., and then comparing the output of our FLAASH tool to the output provided by the FLAASH authors for those images.
During the development of FLAASH, Spectral Sciences, Inc. collected ground spectra for dark to light calibration panels, as well as numerous real surfaces such as roads and dry lake beds, and compared FLAASH-corrected spectra to them. They found that the FLAASH-corrected spectra were the same as the ground-collected spectra within the uncertainty of the ground truth measurements.
As a test of the numerical accuracy, Spectral Sciences, Inc. also performed reflectance retrievals on simulated data cubes using the same model atmosphere and viewing geometry assumed for the simulation. The results are very close to the original reflectances. With no adjacency corrections in either the retrieval or simulation directions the original reflectances are reproduced very precisely (to within 0.001 outside extremely strong atmospheric absorption regions).
FLAASH References
Adler-Golden, S. M., M. W. Matthew, L. S. Bernstein, R. Y. Levine, A. Berk, S. C. Richtsmeier, P. K. Acharya, G. P. Anderson, G. Felde, J. Gardner, M. Hoke, L. S. Jeong, B. Pukall, A. Ratkowski, and H.-H Burke, 1999. Atmospheric Correction for Short-wave Spectral Imagery Based on MODTRAN4. SPIE Proceedings on Imaging Spectrometry, Vol. 3753, pp. 61-69.
Berk, A., L. S. Bernstein, G. P. Anderson, P. K. Acharya, D. C. Robertson, J.H. Chetwynd, and S. M. Adler-Golden, 1998. MODTRAN Cloud and Multiple Scattering Upgrades with Application to AVIRIS. Remote Sensing of the Environment, Vol. 65, pp. 367-375.
Berk A., L. S. Bernstein, and D. C. Robertson, 1989. MODTRAN: a moderate resolution model for LOWTRAN7. GL-TR-89-0122. Air Force Geophysical Laboratory, Hanscom AFB, MA. p. 38.
Matthew, M. W., S. M. Adler-Golden, A. Berk, S. C. Richtsmeier, R. Y. Levine, L. S. Bernstein, P. K. Acharya, G. P. Anderson, G. W. Felde, M. P. Hoke, A. Ratkowski, H.-H. Burke, R. D. Kaiser, and D. P. Miller, 2000. Status of Atmospheric Correction Using a MODTRAN4-based Algorithm. SPIE Proceedings, Algorithms for Multispectral, Hyperspectral, and Ultraspectral Imagery VI. 4049, pp. 199-207.