title: Diurnal emissivity dynamics in bare versus biocrusted sand dunes.
abstract: Land surface emissivity (LSE) in the thermal infrared depends mainly on the ground cover and on changes in soil moisture. The LSE is a critical variable that affects the prediction accuracy of geophysical models requiring land surface temperature as an input, highlighting the need for an accurate derivation of LSE. The primary aim of this study was to test the hypothesis that diurnal changes in emissivity, as detected from space, are larger for areas mostly covered by biocrusts (composed mainly of cyanobacteria) than for bare sand areas. The LSE dynamics were monitored from geostationary orbit by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) over a sand dune field in a coastal desert region extending across both sides of the Israel-Egypt political borderline. Different land-use practices by the two countries have resulted in exposed, active sand dunes on the Egyptian side (Sinai), and dunes stabilized by biocrusts on the Israeli side (Negev). Since biocrusts adsorb more moisture from the atmosphere than bare sand does, and LSE is affected by the soil moisture, diurnal fluctuations in LSE were larger for the crusted dunes in the 8.7 μm channel. This phenomenon is attributed to water vapor adsorption by the sand/biocrust particles. The results indicate that LSE is sensitive to minor changes in soil water content caused by water vapor adsorption and can, therefore, serve as a tool for quantifying this effect, which has a large spatial impact. As biocrusts cover vast regions in deserts worldwide, this discovery has repercussions for LSE estimations in deserts around the globe, and these LSE variations can potentially have considerable effects on geophysical models from local to regional scales.
authors.affiliation: Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus, 84990, Israel.
authors.forename: Offer
authors.initials: O
authors.lastname: Rozenstein
authors.affiliation: Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus, 84990, Israel.
authors.forename: Nurit
authors.initials: N
authors.lastname: Agam
authors.affiliation: School of Engineering and CNISM, Potenza Research Unit, University of Basilicata, Potenza, Italy.
authors.forename: Carmine
authors.initials: C
authors.lastname: Serio
authors.affiliation: School of Engineering and CNISM, Potenza Research Unit, University of Basilicata, Potenza, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Masiello
authors.affiliation: School of Engineering and CNISM, Potenza Research Unit, University of Basilicata, Potenza, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Venafra
authors.affiliation: ITRES Research Ltd. #110, 3553 31st Street, N.W. Calgary, Alberta T2L 2K7, Canada.
authors.forename: Stephen
authors.initials: S
authors.lastname: Achal
authors.affiliation: Defence Research and Development Canada (DRDC) - Valcartier, 2459 de la Bravoure, Québec, QC G3J 1X5, Canada.
authors.forename: Eldon
authors.initials: E
authors.lastname: Puckrin
authors.affiliation: Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boker Campus, 84990, Israel. Electronic address: karnieli@bgu.ac.il.
authors.forename: Arnon
authors.initials: A
authors.lastname: Karnieli
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D003889:Desert Climate; D017753:Ecosystem; D004534:Egypt; D004777:Environment; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry; D008962:Models, Theoretical
keywords: Biocrust; LWIR; SEVIRI; Sand dunes; Thermal remote sensing; Water vapor adsorption