Estimating the broadband longwave emissivity of global bare soil from the MODIS shortwave albedo product

Abstract

A constant land surface longwave emissivity value, or very simple parameterization, has been adopted by current land surface models because of a current lack of reliable observations. Of all the various Earth surface types, bare soil has the highest variations in broadband emissivity (BBE). We propose here a new algorithm to estimate BBE in the 8–13.5 µm spectral range based on the Moderate Resolution Imaging Spectrometer (MODIS) albedo product for bare soil. This algorithm takes advantage of both Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) longwave emissivity and MODIS shortwave albedo products, as well as the established linear relationship between ASTER BBE and seven MODIS spectral albedos for bare soil. In order to mitigate step discontinuities in the global land surface BBE product, a transition zone was established and the BBE estimation method was also provided. Three linear formulae were derived for bare soil and transition zones, respectively. Given the accuracy of 0.01 for MODIS spectral albedo, the absolute accuracy of BBE retrieval is better than 0.017. The validation results obtained from the three field trials conducted in China and one field trial in western/southwestern U.S. indicated that the average difference between the estimated BBE and the measured BBE was 0.016. We have introduced a new strategy to generate global land surface BBE using MODIS data. This strategy was used to generate global 8 day 1 km land surface BBE products from 2000 through 2010.

A long-term Global LAnd Surface Satellite (GLASS) data-set for environmental studies

“…The broadband emissivity derived from the MODIS albedos was validated by the field measurements conducted over desert areas in the USA and China; the absolute difference was found to be 0.02 (Cheng and Liang 2013b). The broadband emissivity derived from the AVHRR was consistent with that derived from MODIS data.…”

“…GLASS emissivity algorithms (Cheng and Liang 2013b;Ren et al 2013) classify the land surface into five types: water, snow/ice, bare soils, vegetated areas, and transition zones. The first two surface types are derived from the preprocessing steps and their emissivity values are set at 0.985 based on the ASTER spectral library (http://spclib.jpl.nasa.gov) and the MODIS UCSB spectral library (http://www.icess.ucsb.edu/modis/EMIS/html/em.html).…”

A Comparative Study of Three Land Surface Broadband Emissivity Datasets from Satellite Data

“…Long time series of high spatial-temporal global land surface BBE will benefit the studies of surface energy budget. Cheng et al, [27,28] proposed the algorithms for retrieving global land surface BBE from the Advanced Very High-Resolution Radiometer (AVHRR) and MODIS optical data, and produced the global eight-day 1 km and 0.05° land surface BBE from 1981 through 2010. This product was known as the Global Land Surface Satellite (GLASS) BBE and released to public in November 2012 [29], and can be ordered from the BNU Center for Global Change Data Processing and Analysis (http://www.bnu-datacenter.com) and Global Land Cover Facility (http://glcf.umd.edu).…”

Estimating Land Surface Temperature from Feng Yun-3C/MERSI Data Using a New Land Surface Emissivity Scheme

“…The GLASS BBE product [37] was derived from the Advanced Very High Resolution Radiometer (AVHRR) and MODIS data using the newly developed algorithms [38,39]. The GLASS LAI product was generated using a general regression neural network (GRNN) from the MODIS surface reflectance data [40].…”

“…We can infer from this that the soil background emissivity underneath the vegetation canopy is stable, based on Figure 6. According to the validation using four field trials by Cheng et al [39], the accuracy of the GLASS BBE of bare soil is 0.016, and so the mean soil emissivity can be used to represent the soil background emissivity underneath the vegetation canopy. Second, using only one formula to regress the relationship between the GLASS BBE and estimated LSE may introduce some errors.…”