Study of Some Lakes in the North-Eastern Romanian Plain Using the Coherence Image of the Tandem Pair (ERS-1 and ERS-2)

Abstract

In radar SAR interferometry (InSAR/DinSAR), a Tandem pair (ERS-1/2) is used for the realization of a DEM or the detection of deformations of a major event (e.g. earthquake) occurring between two acquisitions. The advantage of the Tandem pair is the time interval of 24 hours between the two captures. Generally, there is no temporal decorrelation considering the small difference in time between the acquisitions, which results in a good coherence. The coherence image is used indirectly in radar SAR interferometry as an indicator of the levels of confidence of the interferograms. It can be used in a direct way to identify and delimit the various movement zones which disturb the phase of the radar wave. The objective of this work is to show the utility and the effectiveness of the coherence image in the cartography of lakes and vegetation in a region at the Curvature of the Romanian Carpathians 1 . Between the two acquisitions dates of May 28 and 29, 1995, there was no geological process involving displacements in direction of the radar. This pair represents the only one among the other pairs which gave a good coherence for the whole scene. In the flat part, one notes a good coherence except for the lakes. They are well represented by very dark colours with zero coherence. In the part of high altitude, especially where there is vegetation, a bad coherence can be clearly seen. Using this image (coherence), one could distinguish the parts with vegetation in great movements due to the effects of the wind, therefore characterised by 1 In this paper "the Curvature of the Romanian Carpathians" refers to a broader area which includes the Curvature Carpathians and Subcarpathians as well as the outer plain units. K. Hachemi et al. 24great heights. The coherence image thus makes it possible to delimit two natural elements in this area, the lakes and the vegetation. The lakes are well delimited, in particular when they are full as in the rain seasons. To show this utility and this effectiveness of the coherence image, we measured the surfaces and dimensions of the lakes based on the Tandem pair and to make a comparison with the existing data and to interpret the results obtained. The three lakes, located in the plain to the East and North-East of the Buzău town, clearly appear in the coherence image.

Temporal Coherence Changes of Typical Urban Features Based on Sentinel-1A Data

“…In recent years, with the improvement of sensor technology and the quality of sensing data, remote sensing has become an important technique for obtaining geospatial information. Remote sensing can not only rapidly and synchronously acquire spatial data over a large area and measure and produce topographic maps of various scales and other spatial information products, but also be used for digital elevation model (DEM) production, (1)(2)(3) surface deformation inversion, (4)(5)(6)(7) land use type classification, (8)(9)(10) forest biomass mapping, (11,12) and terrain slope information extraction. (13) Recently, higher requirements have been placed on the acquisition of remote sensing information and information-processing technology.…”