Radar observations of planetary dune analogues and assessing their stability using synthetic aperture radar. Conference Paper uri icon

abstract

  • Introduction: Monitoring geomorphic changes on other planets is always a puzzle while on Earth measur-ing geomorphological dynamics can involve field work, i.e., ground truth. Dunes, wind streaks and other aeolian morphologies have been identified on Earth, Mars, Venus and Titan. These morphologies can be subjected to rapid and continuous changes when the surface is not stabilized by vegetation or crust and the wind is sufficiently strong. Thus, these sand bodies can change rapidly responding to the wind regime, rainfall, and sand particle availability. Identifying these changes by remote sensing (or even on the ground) is not straightforward because the entire surface may change concurrently. In this paper we demonstrate how synthetic aper-ture radar interferometry (InSAR) can be used to iden-tify changes in dunes using the coherence which is normally a measure of phase noise prohibiting interfer-ometric studies. We demonstrate this for dunes along the Negev and Sinai border region. This paper will show how ERS data were used to map the stability, and loss of it, over time ranges spanning from 1 day inter-vals to 2 years when eventually the entire surface changed including the, so called, stable areas. This methodology has advantages as it does not show poten-tial mobility but rather the true mobility or stability. It is applicable to planetary landscapes where there is no other indication of stability. Moreover, the methodol-ogy can be used also to measure the stability of surfac-es susceptible to other mechanisms of landscape changes. Synthetic aperture radar: Synthetic-aperture radar (SAR) is a method for the acquisition of images by actively illuminating a target scene with microwaves (~ 1 cm to 1 m) and integrating multiple radar images along a flight track to yield higher-resolution images than would be possible by a real aperture radar anten-na. SAR amplitude images provide information on the surface geometry including slopes and roughness and the surface dielectric constant. Spaceborne platforms such as ERS, and Radarsat, and the previously flown 1994 SIR-C/X-SAR exhibit single-look resolutions of 5-8 m in range and 15-20 m in azimuth and new spaceborne platforms such as the German TerraSAR-X, the Israeli TecSAR, and the Ital-ian Comos Sky-med all exhibit resolution capibilities of at least 1 m. Mostly, data are processed to multilook images, which are produced by averaging single imag-es of the same area to create a reduced speckle image (with lower spatial resolution.) Hence, the SAR spatial resolutions is as fine and at times superior to those known on current civilian VIS/NIR platforms and pro-vide complementary information about the target sce-ne. Another advantage of SAR system is the ability to acquire observations during both day and night and through all weather conditions, the results are systemat-ic observation of the area of interest. Radar coherence The radar phase is also affected by other factors, which together make the raw SAR phase image essentially arbitrary, with no correlation from pixel to pixel. Coherence is one of the products of the SAR interferometric process and it represents the magnitude of the complex corre-lation of both amplitude and phase information from two interferometric signals. The coherence is used to measure interferometry SAR data quality. Because each pixel in a SAR image is formed by the coherent sum of the backscatter from thousands of cells on the scale of the radar wavelength, temporal decorrelation can also be caused by the relative motion of the scattering cells within the SAR resolution (for

publication date

  • June 1, 2012