Evaluation of Insar Dem from High-Resolution Spaceborne Sar Data (original) (raw)
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DIGITAL ELEVATION MODEL (DEM) GENERATION FROM SAR INTERFEROMETRY
SAR Interferometry (InSAR) provides data that contain information relating to the phase and coherence components of the backscattered radar signals. Phase information is used to derive Digital Elevation Models (DEM). This paper presents the results of an analysis of the accuracy of InSAR DEM derived from ESAR L-band airborne repeat-pass fully polarimetric InSAR data, which were acquired over Thetford Forest, in the east of England. An area with no tree cover of about 300m by 300m in size was chosen as a test site. Then InSAR DEMs for L-band HH, HV and VV polarisations were generated. The accuracy of the InSAR-derived DEMs was deduced by comparison with reference DEMs, which were generated from field data acquired from both Global Positioning System (GPS) & spot height survey and a Lidar DEM. The Lidar DEM was acquired by the UK Environment Agency. The poster reports the results of these comparisons and some concluding remarks about the relationship between the accuracy of the InSAR DEMs, polarization mode, and the nature of the ground surface cover are highlighted.
In recent years, Synthetic Aperture Radar (SAR) data have been widely used for scientific applications and several SAR missions were realized. The active sensor principle and the signal wavelength in the order of centimeters provide all-day and all-weather capabilities, respectively. The modern German TerraSAR-X (TSX) satellite provides high spatial resolution down to one meter.. Based on such data SAR Interferometry may yield high quality digital surface models (DSMs), which includes points located on 3d objects such as vegetation, forest, and elevated man-made structures. By removing these points, digital elevation model (DEM) representing the bare ground of Earth is obtained. The primary objective of this paper is the validation of DEMs obtained from TSX SAR data covering Barcelona area, Spain, in the framework of a scientific project conducted by ISPRS Working Group VII/2 "SAR Interferometry" that aims the evaluation of DEM derived from data of modern SAR satellite sensors. Towards this purpose, a DSM was generated with 10m grid spacing using TSX StripMap mode SAR data and converted to a DEM by filtering. The accuracy results have been presented referring the comparison with a more accurate (10cm-1m) digital terrain model (DTM) derived from large scale photogrammetry. The results showed that the TSX DEM is quite coherent with the topography and the accuracy is in between ±8-10m. As another application, the persistent scatterer interferometry (PSI) was conducted using TSX data and the outcomes were compared with a 3d city model available in Google Earth, which is known to be very precise because it is based on LIDAR data. The results showed that PSI outcomes are quite coherent with reference data and the RMSZ of differences is around 2.5m.
DEM by Ground-Based SAR Interferometry
IEEE Geoscience and Remote Sensing Letters, 2000
In this letter, a ground-based synthetic aperture radar (SAR) interferometer was used to generate digital elevation maps (DEMs) of the illuminated area. With respect to other ground-based data processing techniques, here, the effect of the propagation through the atmosphere is considered. An algorithm similar to multipass satellite SAR techniques was developed in accordance with the phase model used in the ground-based interferometry. Many images taken from different viewing angles were collected and combined to form different interferograms at a test site in Austria. Results from this technique have been compared with an existing geographic model of the test area.
COMPARISION OF ELEVATION DERIVED FROM INSAR DATA WITH DEM FROM TOPOGRAPHY MAP
aars.org
Digital Elevation Models (DEMs) are used in many applications in the context of earth sciences such as in topographic mapping, environmental modelling, rainfall-runoff studies, landslide hazard zonation, seismic source modelling, etc. During the last years multitude of scientific applications of Synthetic Aperture Radar Interferometry (InSAR) techniques have evolved. It has been shown that InSAR is an established technique of generating high quality DEMs from spaceborne and airborne data, and that it has advantages over other methods for the generation of large area DEM. However, the processing of InSAR data is still a challenging task. This paper describes InSAR operational steps and processing chain for DEM generation from Single Look Complex (SLC) SAR data and compare a satellite SAR estimate of surface elevation with a digital elevation model (DEM) from Topography map. The operational steps are performed in three major stages: Data Search, Data Processing, and product Validation. The Data processing stage is further divided into five steps of Data Pre-Processing, Co-registration, Interferogram generation, Phase unwrapping, and Geocoding. The Data processing steps have been tested with ERS 1/2 data using Delft Object-oriented Interferometric (DORIS) InSAR processing software. Results of the outcome of the application of the described processing steps to real data set are presented.
CRUCIAL POINTS OF INTERFEROMETRIC PROCESSING FOR DEM GENERATION USING HIGH RESOLUTION SAR DATA
Data collection for digital elevation model (DEM) generation can be carried out by two main methods in space-borne remote sensing such as stereoscopy using optical or radar satellite imagery (stereophotogrammetry, respectively radargrammetry) and interferometry based on interferometric synthetic aperture radar (InSAR) data. These techniques have advantages and disadvantages in comparison against each other. Especially filling the gaps which arise from the problem of cloud coverage in DEM generation by optical imagery, InSAR became operational in recent years and DEMs became the most demanded interferometric products. Essentially, in comparison, DEM generation from synthetic aperture radar (SAR) images is not a simple manner like generation from optical satellite imagery. Interferometric processing has several complicated steps for the production of a DEM. The quality of the data set and used software package come into prominence for the stability of the generated DEM. In the paper, the interferometric processing steps for DEM generation from InSAR data and the crucial threshold values are tried to be explained. For DEM generation, a part of Istanbul (historical peninsula and near surroundings) was selected as the test field because of data availability. The data sets of two different imaging modes (StripMap ~ 3 m resolution and High Resolution Spotlight ~ 1 m resolution) of TerraSAR-X have been used. At the implementation, besides the determination of crucial points at interferometric processing steps, to define the effect of computer software, DEM production have been performed using two different software packages in parallel and the products have been compared In the result section of the paper, besides the colorful visualizations of final products along with the height scales, accuracy evaluations have been performed for both DEMs with the help of a more accurate reference digital terrain model (DTM). This reference model has been achieved by large scale aerial photos. Normally, it has a 5 m original grid spacing, however it has been resampled at a spacing of 1 m towards the needs of the research.
Accuracy assessment of DEMs derived from multi-frequency SAR images
Digital elevation model (DEM) is useful for land surface terrain analysis and is an important requirement for topographic correction of SAR backscatter data in hilly region. SAR interferometric (InSAR) techniques are very useful for deriving DEM of a large patch of land area with considerable accuracy in a faster and cost-effective manner. Today, various orbital radars operating in different frequencies and orbital periods are capable of providing data suitable for interferometric analysis. In the present study we have generated DEMs of Jharia coalmine region, India using InSAR techniques from ALOS-PALSAR, Radarsat-2 data and compared them with SRTM (Shuttle Radar Topography Mission) DEM and then, validated the DEMs against DGPS elevations measured as Ground Control Points (GCPs). We have then attempted to use the InSAR generated high resolution DEM for topographic corrections of SAR backscatter data. Index Terms-Digital elevation model (DEM); SAR Interferometry; Multi-frequency SAR; DGPS I.
Quality assessment of interferometric SAR DEMs
2000
A new interferometric SAR (InSAR) procedure for DEM generation was employed to generate different DEMs from ERS SAR image pairs. The procedure was validated comparing the InSAR DEMs with a suited reference DEM. In the first part of the paper the principal features of the procedure are briefly summarised. The second part is focused on the quality assessment of the InSAR DEMs. They cover the same test area and come from one ascending SAR image pair, one descending pair and from the fusion of data coming from ascending and descending images. The analysis includes the influence of the SAR image coherence, the degradation of the DEM quality related to the terrain topography and the artefacts due to atmospheric effects.
International Journal of Remote Sensing, 2006
Repeat-pass synthetic aperture radar interferometry (InSAR) appears to be an excellent tool for generating digital elevation models (DEMs) of high spatial and vertical resolution. However, in recent years, it has been noticed that the atmosphere causes errors in the elevation accuracy. The objective of this paper is to try to identify climatic regions in India where InSAR can be used for generating DEMs. A detailed study was carried out to quantify atmospheric effects on the DEMs derived from repeat-pass InSAR. Three test sites were selected for the analysis: one over Mumbai, which is a part of the western ghats region with hilly terrain, lakes and forests; another is the Kolar area with gently undulating terrain with agricultural and forested lands; and the last was Bhuj, an arid plains region which is close to the Rajasthan Thar desert, India. Six interferograms of the Bhuj area derived from two tandem pairs were analysed and it was found that there were varying atmospheric effects of the order of 0.2l to 1l and at specific locations more than l. In the case of the Mumbai and Kolar study areas with two interferograms each, the atmospheric effects were almost negligible. In these cases, it is shown that it was also possible to estimate the height of buildings to an accuracy of 1-2 m. Therefore, it is concluded that one should be cautious when using InSAR techniques for generating DEMs of desert/ arid regions where the climate may be very dynamic and only small amounts of water vapour can cause strong atmospheric artefacts.
Quality assessment of InSAR digital elevation models
A nearly worldwide digital elevation model (DEM) has been generated by the Shuttle Radar Topography Mission (SRTM) with the US C-band by single-pass Interferometry. This height model is available free of charge with a spacing of 3 arcsec corresponding to 92 m  70 m in the test area. On the SRTM beside the US C-band also the German-Italian X-band was active, but not in the scan SAR (Synthetic Aperture Radar) mode. By this reason the X-band DEM has gaps between the covered flight lines. The DEMs generated by the German Aerospace Center DLR are not free of charge, but they do have the advantage of a spacing of just 1 arcsec corresponding to 31 m  23 m in the test area. In the area of Zonguldak SRTM C-band and X-band DEMs are available and have been analyzed in detail in relation to a sufficient accurate reference DEM as well as C-band data with 1 and 3 arcsec spacing in the USA. The SRTM-DEMs have a standard deviation in flat and open areas of approximately 3 m to 5 m. The accuracy is depending upon the terrain inclination, vegetation and buildings. The short C-band as well as the X-band radar cannot penetrate the vegetation, so in the forest area the height of the visible surface will be achieved, reducing the quality. The influence of buildings to the height model can be eliminated by filtering if the area is not too mountainous.
Sensors
Digital elevation model (DEM) plays a vital role in hydrological modelling and environmental studies. Many essential layers can be extracted from this land surface information, including slope, aspect, rivers, and curvature. Therefore, DEM quality and accuracy will affect the extracted features and the whole process of modeling. Despite freely available DEMs from various sources, many researchers generate this information for their areas from various observations. Sentinal-1 synthetic aperture radar (SAR) images are among the best Earth observations for DEM generation thanks to their availabilities, high-resolution, and C-band sensitivity to surface structure. This paper presents a comparative study, from a hydrological point of view, on the quality and reliability of the DEMs generated from Sentinel-1 data and DEMs from other sources such as AIRSAR, ALOS-PALSAR, TanDEM-X, and SRTM. To this end, pair of Sentinel-1 data were acquired and processed using the SAR interferometry techniq...