The Application of ALOS/PALSAR InSAR to Measure Subsurface Penetration Depths in Deserts

Siting Xiong,Jan-Peter Muller,Gang Li

doi:10.3390/rs9060638

Abstract

Spaceborne Synthetic Aperture Radar (SAR) interferometry has been utilised to acquire high-resolution Digital Elevation Models (DEMs) with wide coverage, particularly for persistently cloud-covered regions where stereophotogrammetry is hard to apply. Since the discovery of sand buried drainage systems by the Shuttle Imaging Radar-A (SIR-A) L-band mission in 1982, radar images have been exploited to map subsurface features beneath a sandy cover of extremely low loss and low bulk humidity in some hyper-arid regions such as from the Japanese Earth Resources Satellite 1 (JERS-1) and Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR). Therefore, we hypothesise that a Digital Elevation Model (DEM) derived by InSAR in hyper-arid regions is likely to represent a subsurface elevation model, especially for lower frequency radar systems, such as the L-band system (1.25 GHz). In this paper, we compare the surface appearance of radar images (L-band and C-band) with that of optical images to demonstrate their different abilities to show subsurface features. Moreover, we present an application of L-band InSAR to measure penetration depths in the eastern Sahara Desert. We demonstrate how the retrieved L-band InSAR DEM appears to be of a consistently 1–2 m lower elevation than the C-band Shuttle Radar Topography Mission (SRTM) DEM over sandy covered areas, which indicates the occurrence of penetration and confirms previous studies.

Highlights

Hyper-arid regions remain one of the most desolate and inhospitable places on Earth
Radar Topography Mission (SRTM) Digital Elevation Models (DEMs) over sandy covered areas, which indicates the occurrence of penetration and confirms previous studies
Red arrows in the Landsat images (Figure 5a,d) point out three noteworthy areas. They are likely to be sand dunes, which are recognisable in the Shuttle Radar Topography Mission (SRTM) C-band amplitude image (Figure 5b), but cannot be observed in the ALOS/PALSAR image (Figure 5e)

Summary

Introduction

Some of them host many subsurface natural resources, such as oil, gas, groundwater, etc. The exploitation of these subsurface resources needs substantial reconnaissance work, such as field surveys and in-situ measurements, which can be very time and labour consuming and costly. L-band SAR images by SEASAT in 1978 [1] led to several follow-up missions: SIR-A (1981), SIR-B (1984), and two SIR-C/X-SAR missions (1994). These missions revealed that at L-band wavelengths, radar has a limited penetration ability over the Eastern Sahara [2], coverage with penetration was very limited

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