Interpreting the Browse ProductsCRISM browse products are intended to provide a high-level overview of the contents of calibrated image data, and are not meant for quantitative analysis or to be interpreted with an awareness of possible false detections due to illumination or instrumental effects. However, every effort was made in the construction of the browse products to preserve useful information and the dynamic range of the original calibrated data. In addition, the mapping information specified with the map/stretch information for each product is sufficient to register the browse images with other data sets. Typically registration errors are about 200 m or less. Two versions of the data provide an overview of surface brightness. vnir_rgb is enhanced color over the visible range, and ir_ira is brightness at a wavelength near 1330 nm. Compositional information on the surface is concentrated in four of the browse products (vnir_fem, ir_maf, ir_phy, and ir_hyd). Not all of the sites exhibit spectral evidence for mineralogical diversity. If a location is covered in dust, it appears red in vnir_fem and bland in the other products. Sites with diversity in igneous mineralogy will appear interesting in ir_maf. Sites with minerals formed by interaction of crustal rocks with liquid water will appear interesting in ir_phy and ir_hyd. Sites that have water ice on the surface or as clouds will appear pink, yellow or green in ir_ice, whereas those with carbon dioxide frost on the surface will appear bluish. In addition to those caveats, many of the parameters in the latter four browse products have dependencies on solar incidence angle, surface slopes, atmospheric conditions, detector artifacts, and response to phases other than what the products were intended to show. For example, ir_phy and ir_hyd can have bluish colors due to spectral effects of water ice, either as surface frosts or atmospheric hazes. Illumination geometry or atmospheric dust and ice hazes can create artifacts in vnir_fem, ir_maf, ir_phy, and ir_hyd. ir_phy is particularly susceptible to detector artifacts. An excellent reference describing the parameters used in constructing vnir_fem, ir_maf, ir_phy, ir_hyd, and ir_ice is: Pelkey, S. M., J. F. Mustard, S. Murchie, R. T. Clancy, M. Wolff, M. Smith, R. Milliken, J.-P. Bibring, A. Gendrin, F. Poulet, Y. Langevin, and B. Gondet, CRISM multispectral summary products: Parameterizing mineral diversity on Mars from reflectance, J. Geophys. Res., 112, E08S14, doi:10.1029/2006JE002831, 2007. |
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