Abstract
Abstract. Maps of backscatter anisotropy parameters from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Advanced Scatterometer (ASCAT), a C-band fan-beam scatterometer, contain unique and valuable data characterising the surface and subsurface of various cryospheric elements, including sea ice and ice sheets. The computational expense and considerable complexity required to produce parameter maps from the raw backscatter data inhibits the wider adoption of ASCAT data. Here, backscatter anisotropy parameter maps gridded at a resolution of 12.5 km per pixel are made available to the community in order to facilitate the exploitation of these parameters for cryospheric applications. These maps have been calculated from the EUMETSAT Level 1B Sigma0 product acquired from ASCAT on board MetOp-A, MetOp-B and MetOp-C. The dataset is unique in that it prioritises anisotropy characterisation over temporal resolution and combines ASCAT data from multiple platforms. The parameterisation chosen assumes a linear falloff of backscatter with incidence angle and a fourth-order Fourier series parameterisation of azimuth angle anisotropy. The product (Fraser and Cartwright, 2022) is available at https://doi.org/10.26179/91c9-4783 presented on three timescales depending on orbital platform availability: 5 d (2007 to 2020 – MetOp-A only – suitable for users requiring a long time series), 2 d (2013 to 2020 – MetOp-A and MetOp-B) and 1 d resolution (2019–2020 – MetOp -A, MetOp-B and MetOp-C – suitable for users needing both high temporal resolution and detailed anisotropy characterisation). Datasets will be updated annually.
Highlights
Observation and characterisation of the polar cryosphere is of critical importance in understanding changes to the Earth’s climate system
Such structured alignment is commonly encountered in sand dune systems, in croplands (Bartalis et al, 2006) and over the Greenland and Antarctic ice sheets, in the form of sastrugi (Long and Drinkwater, 2000)
Fan-beam scatterometers use multiple fixed antennae at different orientations, allowing for multiple looks at each pixel in a swath-like signal. This configuration combined with the spacecraft orbit means that over a given time interval, backscatter from a point on the surface is measured from a wide variety of both incidence (∼ 25 to 65◦ for Advanced Scatterometer (ASCAT)) and azimuth angles
Summary
Observation and characterisation of the polar cryosphere is of critical importance in understanding changes to the Earth’s climate system. The extent, variability and physical characteristics of snow and ice (and their trends), both grounded and floating, have far-reaching climatic consequences and can respond relatively rapidly to changes in atmospheric and oceanic forcing (IPCC, 2019). J. Cartwright et al.: Polar maps of backscatter parameters from ASCAT and parts of the Antarctic Ice Sheet are undergoing profound changes in response to atmospheric and oceanic forcing, in the form of enhanced melt (both supraglacial and subglacial in ice shelf cavities), resulting in mass loss and contributions to sea-level rise (Holland et al, 2019; Shepherd et al, 2020). We draw attention to the useful physical characteristics which can be retrieved by non-nadir C-band (∼ 5 GHz) radar backscatter cross section (hereafter “backscatter”) in order to provide context for the interpretation of the dataset accompanying this paper
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