ERS-ENVISAT Cross-interferometry for Coastal DEM Construction
Sang-Hoon Hong(1) and Joong-Sun Won(1)
134 Shinchon-dong, Seodaemun-gu,
Korea, Republic of
Digital elevation model (DEM) of a coastal area in a time series can be utilized to monitor changes annually and seasonally. Topographic features in coastal regions change significantly within a relatively short period compared with landmass, but it is difficult to obtain coherent interferometric SAR pairs over coastal areas. ERS-ENVISAT 30-minute tandem pair is very useful to observe coastal regions. We studied an ERS-ENVISAT cross-interferometric pair with a perpendicular baseline of 1.4 km and a height sensitivity of 6 m. The small height ambiguity is favorable to construct a digital elevation model in low relief coastal areas. Accurate coregistration was required because of the differences of the pulse repetition frequency and range sampling rate between the two sensors. Resampling of ENVISAT ASAR data was first performed to have equivalent pixel spacing to the ERS SAR data. Range and azimuth offset were estimated to a sub-pixel accuracy using image intensity cross correlation. A larger window chip size than a general case was used because it was difficult to distinguish typical features. The 540 Hz difference in Doppler centroid was estimated, and the cross-interferogram was highly coherent. As range bin increased, the difference of Doppler centroid also increased. It resulted in lower coherence in far range than in near range. Coherences over wetland in near and far range were about 0.8 and 0.5, respectively. The coherence was improved by applying azimuth and range common band filtering, but coherence gap still existed. ERS-ENVISAT cross-interferogram usually lost information in urban area. However, coherence over a city in this pair was about 0.5 because of less man-made structures than other major cities. Accuracy of the DEM constructed by the ERS-ENVISAT 30-minute pair in a coastal area is to be evaluated.