Subsetting of samples is a promising avenue of research for the continued improvement of prediction models for soil properties with diffuse reflectance spectroscopy. This study examined the effects of subsetting by soil total carbon (Ct) content, soil order, and spectral classification withk-means cluster analysis on visible/near-infrared and mid-infrared partial least squares models forCtprediction. Our sample set was composed of various Hawaiian soils from primarily agricultural lands withCtcontents from <1% to 56%. Slight improvements in the coefficient of determination (R2) and other standard model quality parameters were observed in the models for the subset of the high activity clay soil orders compared to the models of the full sample set. The other subset models explored did not exhibit improvement across all parameters. Models created from subsets consisting of only lowCtsamples (e.g.,Ct< 10%) showed improvement in the root mean squared error (RMSE) and percent error of prediction for lowCtsoil samples. These results provide a basis for future study of practical subsetting strategies for soilCtprediction.
[1] Twenty-one craters in southwestern Margaritifer Terra exhibit unusually warm interior deposits in nighttime Thermal Emission Imaging System (THEMIS) infrared images. These deposits exhibit nighttime temperatures as high as 223 K and are 5-18°warmer than the surrounding plain. Thermal inertia values, derived from Thermal Emission Spectrometer (TES) data, are greater for the deposits than the plains, with maximum values between $455 and 675 J m À2 K À1 s À1/2 . Analysis of THEMIS thermal inertia data having nearly an order of magnitude better spatial resolution shows that the deposits can have a thermal inertia as high as $1060 J m À2 K À1 s À1/2 . Albedo and dust cover index values suggest that both the deposits and the surrounding region are generally dustfree. Compositional analysis with TES and THEMIS data show that though a small number of the deposits may have isolated compositional differences, the majority of the deposits have a composition similar to that of the surrounding plains. The geomorphology of the craters as viewed from Mars Orbiter Camera (MOC) images shows that the deposits are coherent units, rather than sand deposits, an observation that is consistent with the relatively high thermal inertia values. If these deposits are coherent rock units, as the results of our study suggest, possible methods of formation include emplacement of primary igneous material or lithification of sediments from surrounding terrain.
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