Diurnal variation in Sahara desert sand emissivity during the dry season from IASI observations

Abstract

The problem of diurnal variation in surface emissivity over the Sahara Desert during non-raining days is studied and assessed with observations from the Infrared Atmospheric Sounding Interferometer (IASI). The analysis has been performed over a Sahara Desert dune target area during July 2010. Spinning Enhanced Visible and Infrared Imager observations from the European geostationary platform Meteosat-9 (Meteorological Satellite 9) have been also used to characterize the target area. Although the amplitude of this daily cycle has been shown to be very small, we argue that suitable nighttime meteorological conditions and the strong contrast of the reststrahlen absorption bands of quartz (8–14 μ m) can amplify its effect over the surface spectral emissivity. The retrieval of atmospheric parameters show that at nighttime an atmospheric temperature inversion occurs close to the surface yielding a thin boundary layer which acts like a lid, keeping normal convective overturning of the atmosphere from penetrating through the inversion. This mechanism traps water vapour close to the land and drives the direct adsorption of water vapour at the surface during the night. The diurnal variation in emissivity at 8.7 μ m has been found to be as large as 0.03 with high values at night and low values during the day. At 10.8 μ m and 12 μ m the variation has the same sign as that at 8.7 μ m, but with a smaller amplitude, 0.019 and 0.014, respectively. The impact of these diurnal variations on the retrieval of surface temperature and atmospheric parameters has been analyzed

A Synergetic Algorithm for Mid-Morning Land Surface Soil and Vegetation Temperatures Estimation Using MSG-SEVIRI Products and TERRA-MODIS Products

“…Meanwhile, as introduced by Li et al [64], an uncertainty of 1% in the emissivity in the reference channel (12 μm) can result in an error of about 0.5 K in LST. Recent research also showed the diurnal variation in surface emissivity during non-raining days [52,65,66]. Therefore, the simple setting of soil and vegetation emissivity in the study also will bring inevitable errors in soil and vegetation temperature estimation.…”

Kalman filter physical retrieval of surface emissivity and temperature from SEVIRI infrared channels: a validation and intercomparison study

“…The transform has been successfully used with emissivity retrieval for IASI Masiello et al, 2014) and SEVIRI (Masiello et al, 2013b).…”

“…The remapping involves a high-spectral-resolution algorithm which is first applied to the 10-hinge-point UW/BFEMIS emissivities to generate the emissivity spectrum, which, in turn, is convolved with he SEVIRI spectral response. Details of this procedure can be found in Masiello et al (2013bMasiello et al ( , 2014. In passing, we note that the algorithm to transform UW/BFEMIS emissivities to high spectral resolution was first proposed and developed by Borbas and Ruston (2010).…”

“…In addition, KF emissivity products have been intercompared with IASI (Infrared Atmospheric Sounding Interferometer; Hilton et al, 2012) retrievals in Masiello and Serio (2013) and Masiello et al (2014).…”

Surface parameters from SEVIRI observations through a Kalman filter approach: application and evaluation of the scheme in Southern Italy

“…Further details about the UW/BFEMIS emissivity transformation into the SEVIRI channel emissivity are reported in Masiello et al (2014); Serio et al (2013Serio et al ( , 2014.…”