Laboratory for
Climatology and Remote Sensing

Abstract:

The paper is aimed at the retrieval of total column water vapor (TCWV) over a melting glacier using high spatial resolution hyperspectral measurements performed by the German EnMAP (Environmental Mapping and Analysis Program) satellite. Such measurements are important for understanding the intra-pixel variability of water vapor satellite products with coarser spatial resolution especially in regions with drastic changes in the water vapor abundances. The retrieved TCWV is compared with that derived using other spaceborne optical measurements such as performed by Sentinel-5P. The close correspondence of both retrievals has been found with a smaller variance over derived EnMAP TCWV values.

Abstract:

We propose simple analytical equations for the modeling of clean and dusty flat glacier ice surfaces, which can be used to inversely derive the parameters of microstructure of flat bare glacier ice and snow using both ground – based and spaceborne observations of the hyperspectral solar reflectance. The retrievals are based on the asymptotic radiative transfer equations valid for the case of weak light absorption in the semi-infinite turbid medium. The light reflection at the air - ice and ice - air interfaces is fully accounted for. To demonstrate the validity of the approach, the derived equations are exemplarily applied to both ground – based and EnMAP satellite measurements over the Hardangerjøkulen glacier (Norway). A number of important parameters controlling spectral signatures of the snow and glacier ice surfaces have been derived. The ground-based measurements confirm that the theoretical formulation presented in this work can be used to represent the solar light spectral reflectivity of glaciers. The application to satellite hyperspectral imagery shows that this novel technique allows for the determination of the glacier ice albedo (spectral, broadband) based on spaceborne glacier ice reflectance measurement. Additionally, the results demonstrate that not spectrally neutral soot but rather deposited atmospheric dust which enhances the absorption towards UV is responsible for the light absorption by snow for the case studied. Spatial distribution maps of ice grain diameter and dust concentration are derived over the glacier. These findings show that the analytical theory presented in this work can support further research on the characterization and monitoring of glaciers based on current and upcoming hyperspectral remote sensing satellite missions.