Investigating landslides with space-borne Synthetic Aperture Radar (SAR) interferometry

Use of SAR interferometry for detecting and assessing ground subsidence

This letter studies the impact of the use of permanent scatterers (PS) on the distribution of the perpendicular baselines in long-term satellite interferometric synthetic aperture radar surveys. This letter also evaluates the relation between the radar center frequency and the dispersion of the estimates of the elevations of the PS as a function of noise and of the time jitter due to atmospheric disturbances.

Diameters of the orbital tubes in long-term interferometric SAR surveys

Mokpo City, located on the southwestern coast of the Korean Peninsula, has been built on one of the largest areas of reclaimed coastal land in Korea. This reclaimed land is currently experiencing significant ground subsidence due to soil consolidation. We have estimated the subsidence rate of Mokpo City (8 × 8 km) using the synthetic aperture radar interferometry (InSAR) and InSAR permanent scatterer (PSInSAR) techniques to analyze 26 JERS-1 SAR images acquired between 1992 and 1998 and six ENVISAT ASAR images acquired in 2004–2005. Mean subsidence velocity, which was clearly related to reclaimed land, was computed from the JERS-1 PSInSAR analysis. The results indicate a continuous and significant subsidence at three sites (Dongmyung, Hadang and Wonsan), where the subsidence velocity has reached more than 5–7 cm/yr in the area of maximum subsidence. The subsidence rate was found to have decreased in Wonsan and Hadang between 1992 and 1998, while it remained steady or increased in Dongmyung during the same period. The subsidence extended to the period of 2004–2005, and the subsidence rate predicted by the JERS-1 PSInSAR analysis using a linear model was confirmed by the ENVISAT ASAR InSAR results. Our results show that InSAR/PSInSAR-based subsidence maps are useful for the long-term monitoring of soil consolidation and for defining risk zones in coastal reclaimed regions.

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InSAR-based mapping of surface subsidence in Mokpo City, Korea, using JERS-1 and ENVISAT SAR data

TerraSAR-L is the new imaging radar mission of the European Space Agency. The platform, based on the novel Snapdragon concept, is built around the active phase array antenna of the L-band Synthetic Aperture Radar (SAR). Specification of the L-SAR has been guided by careful analysis of the product requirements resulting in a robust baseline design with considerable margins. Besides having a commercial role for the provision of geo-information products, TerraSAR-L will contribute to the Global Monitoring for Environment and Security (GMES) initiative and serve the scientific user community. Interferometry (INSAR) is a key element behind a number of mission objectives. A L-band SAR in a 14-day repeat orbit is an ideal sensor for solid earth applications (earth quake and volcano monitoring, landslides and subsidence) relying on differential interferometry. L-band penetration of vegetation cover facilitates these applications also over vegetated surfaces. Because of the high coherence, L-band is also the preferred frequency for monitoring ice sheet and glacier dynamics. Highly accurate orbit control (orbital tube <100m) and special wideband INSAR modes are required to support these applications globally and systematically. Precise burst synchronisation enables repeat-pass ScanSAR interferometry and global coverage within the short repeat cycle. A feasibility study into cartwheel constellations flying in close formation with TerraSAR-L revealed the potential for generating Digital Elevation Models (DEMs) of unprecedented quality (2m relative height accuracy @ 12m posting). The TerraSAR-L operations strategy is based on a long-term systematic and repetitive acquisition scenario to ensure consistent data archives and to maximise the exploitation of this very powerful SAR system.

https://earth.esa.int/fringe03/proceedings/papers/123_zink.pdf

The TerraSAR-L Interferometric Mission Objectives

Long term interferometry with L band can be studied using data from the Japanese satellite JERS, that flew from 1992 to 1998. Notwithstanding problems like electromagnetic interference and limited information on the across track baselines, still the quality of the system makes the data very useful. This makes it possible the identification of Permanent Scatterers in urban and semi urban areas, with very high density (up to 150/km ) with coherence up to .9 in an interval of time of several years. In turn, this allows the better determination of the orbits, and allows a comparison with similar data from ERS 1. Namely, a similarity is found with data acquired during the 3 days repeat cycle. The longer wavelength therefore is seen to correspond to a longer decay time of the temporal coherence, thus explaining the high quality results obtained. The higher average coherence allows to combine the phase information of several adjacent points, and therefore to at least partially reduce the effects of the higher geometric dispersion of the differential interferometry outcomes due to the very same longer wavelength. In conclusion, while the technique appears too coarse for direct estimation of building motion, it appears very interesting for vegetated areas and for areas where the velocity of the motion would create alias in C band. Introduction The Japanese satellite JERS-1 has been operational from 1992 to 1998. It used a sensor in L band (λ=23,5cm, f0=1.275GHz, 18x6m ground range x azimuth resolution) with polarization HH; it had a sun-synchronous orbit with altitude 568 km. Images were acquired every 44 days. The acquisition angle is 35°, greater than ERS-1, and the foreshortening effect is weaker. Moreover, the orbit is lower and allows getting a resolution higher than in case of ERS. The longer wavelength makes JERS useful for geologic applications in areas covered by vegetation, due to the higher penetration of the signal. Unfortunately, JERS images are affected by various problems (ambiguity in azimuth values, imprecision of the on board clock, low signal to noise ratio, limited information from ephemeredes, etc.) caused by a power loss of the signal transmitted from the platform to the ground. Images are also more sensible to noise due to the interaction with ground radars. Figure 1: C band and L band (SIR-C/X-SAR images of Flevoland in Holland). color scheme: HH: red, HV:green, VV: blue ERS satellites operate in C band with VV polarization, while JERS uses L band with HH polarization. Both ERS and JERS show a strong layover effect. Due to its acquisition geometry, ERS is twice as sensible to the vertical component of displacement as JERS. Figure 2 allows a comparison of the geometric distortions of the two sensors.

https://earth.esa.int/fringe03/proceedings/papers/126_rocca.pdf

K. Daito

Papers

L-band PS Analysis: JERS-1 results and TerraSAR-L predictions

L-band PS analysis: JERS-1 results and TerraSAR - L predictions