PRISM SURFACE REFLECTANCE PROCESSING AND PRODUCTS
Last Modified 19 October 2013 by D. R. Thompson
Contacts: 
Pantazis Mouroulis, Jet Propulsion Laboratory
Bo Cai Gao, Naval Research Laboratory
Robert O. Green, Jet Propulsion Laboratory
Sarah R. Lundeen, Sarah.R.Lundeen@jpl.nasa.gov
David R. Thompson, David.R.Thompson@jpl.nasa.gov 

The PRISM Level 2 processing pipeline transforms calibrated PRISM L1B radiance data into surface reflectance.  This document describes the algorithm, its theoretical assumptions, and products.   We use reflectance in a generic sense, but acknowledge that this measurement has more specific formulations [Schaepman-Strub 2006]. 

The atmospheric correction is based on the Atmosphere Removal Algorithm (ATREM) program developed by Gao et al. [1993].  It retrieves scaled surface reflectance by modeling the absorption due to water vapor, carbon dioxide, ozone, nitrous oxide, carbon monoxide, methane, and oxygen.  These absorption models are combined with observation geometry to estimate atmospheric transmittance from 380-1000 nanometers.  Scattering effects are modeled with the 6S code [Vermote, 1997].  The algorithm retrieves the integrated water vapor amount on a per-pixel basis using 940 and 1140nm water absorption features, and then estimates the Lambertian surface reflectance.  

The PRISM pipeline adds absorption cross sections from the HITRAN 2012 line list [Rothman 2013], and wavelength calibration adjustments based on positions of the water absorption bands.  Pressure altitude is now retrieved using the depth of the oxygen A band, which improves performance for images with large elevation changes and variable optical path.  Water vapor absorption is calculated using the Oxford Reference Forward Model [Dudhia 2013].  

The products are:
  *_rfl_ort - Surface reflectance scaled by a factor of 10000

References:
Dudhia, A. Reference Forward Model. visited 22 August 2013. 
    http://www.atm.ox.ac.uk/RFM/
Gao, B.C., K. H. Heidebrecht, and A. F. H. Goetz, Derivation of scaled surface 
    reflectances from AVIRIS data, Remote Sens. Env., 44, 165-178, 1993
Mlawer E. J., et al.. Development and recent evaluation of the MT_CKD model of 
    continuum absorption. Phil. Trans. Royal Soc. A, 370, 2012.
Rothman, L. S. et al., The HITRAN 2012 molecular spectroscopic database. Journ.
    Quant. Spectroscopy and Radiative Transfer,  2013 (in press).
Schaepman-Strub, G., Schaepman, M. E., Painter, T. H., Dangel, S. and  
    Martonchik, J. V.  Reflectance quantities in optical remote sensing 
    definitions and case studies. Remote Sensing of Environment, 103, 27-42, 
    2006.
Vermote, Eric F., et al. Second simulation of the satellite signal in the solar 
    spectrum, 6S: An overview. IEEE Trans. Geosci. Remote Sens. 35.3. 675-686,
    1997.