Yusen Dong

Radar backscatter analysis for urban environments

Abstract A full understanding of radar backscatter from urban areas is necessary in order to develop a robust methodology for monitoring and classifying urban characteristics using remotely sensed Synthetic Aperture Radar images.This paper examines the dominant backscattering mechanisms such as single bounce from roofs, double bounce from wall-ground structures and possibly triple bounce from wall-wall-ground structures, and their relative contributions to the backscatter. With the use of quad-polarized image data such as those acquired by the NASA/JPL AirSAR system, the backscatter can be decomposed into components caused by different backscattering mechanisms, offering a promise for urban monitoring and classification.

Comparison of radar image segmentation by Gaussian- and Gamma-Markov random field models

This paper compares segmentation results of synthetic aperture radar (SAR) images using Gaussian-Markov random field (MRF) and Gamma-MRF models. A Gamma distribution function is more accurate and proper to trace the multilook SAR intensity data distribution. However, it is found that, at least from examples used in the paper, when the distribution function is incorporated with the MRF model to implement SAR image segmentation, the Gamma-MRF model is not necessarily shown to be superior to the Gaussian-MRF model. Occasionally the Gamma-MRF model wrongly merges a few small segments, suggesting that the Gaussian-MRF model might be more stable and reliable.

Preliminary Results of Satellite Radar Differential Interferometry for the Co-seismic Deformation of the 12 May 2008 Ms8.0 Wenchuan Earthquake

Abstract Satellite differential SAR interferometry has been widely accepted as a powerful tool to map co-, post- and inter-seismic deformation since its successful application to the 1992 Landers Earthquake. As soon as the Ms8.0 Wenchuan Earthquake occurred on 12 May 2008 in the Sichuan Province of southwestern China, the Japan Aerospace Exploration Agency tasked its Advanced Land Observing Satellite (ALOS) to respond to the disaster by collecting images. This paper presents the preliminary DInSAR results of co-seismic deformation of the quake observed from two satellite paths of the onboard ALOS/PALSAR sensor with post-seismic images acquired on 19 and 24 May. Results from pixel offset analysis and difference of coherence will also be discussed. The radar mapping is still ongoing because the ruptured seismic fault is more than 300km in length. Each swath of the PALSAR fine beam covers only about a 75km segment of the fault, and it takes 46 days for ALOS to revisit the same site.

Multi-path PALSAR interferometric observations of the 2008 magnitude 8.0 Wenchuan Earthquake

The Satellite Differential Interferometric Synthetic Aperture Radar (DInSAR) has already demonstrated its potential to map co-, post- and inter-seismic deformation. This paper presents an.alysis of the surface-displacement field of the 12 May 2008 magnitude 8.0 Wenchuan Earthquake using the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) DInSAR. Six PALSAR interferograms of paths 471 to 476 are generated. A new approach, which uses the information of overlapping interferograms, has been developed to compensate for orbit error. The main advantage of this approach is that the calculation is performed without the need for phase unwrapping. Once the orbit error has been compensated for, the interferograms are then merged to form a single interferogram. The final mosaic of interferograms demonstrates a much more consistent co-seismic surface-displacement field than the original interferograms.

Estimating the greatest dust storm in eastern Australia with MODIS satellite images

On the 23rd of September 2009, Sydney encountered its most severe dust storm in 70 years. The dusts were originated from the Lake Eyre Basin and elevated and swept across the Australian Capital Territory, New South Wales, and Queensland by gusty winds. Ground air quality observation indicated that the dust particle density was 70 times higher than the normal when the dusts struck Sydney. The authors have researched MODIS satellite optical imagery in order to monitor this severe dust storm, and have extracted the information from the satellite images through computing the brightness temperature difference of two thermal infrared channels of MODIS imagery. This method is effective in separating dust and clouds. The mass of the dust plume, therefore, has been estimated using a retrieval model. However, the result of the mass is believed to be under-estimated because the extent of dusts was too great to be covered by a single MODIS image.

Understanding of partial polarization in polarimetric SAR data

Abstract Partial polarization is common in multi-look polarimetric images, although a polarimetric radar measures the complete scattering matrix of a target. This Letter indicates how the partial polarization arises, discusses the relationships between the coefficient of variation and partial polarization, and shows that the degree of polarization can be expressed by other quantities such as co- and cross-polarized backscattering coefficients, σ hh 0, σ vv 0 and σ vh 0.

The application of wavelet transform for speckle suppression in radar imagery

An effective algorithm for speckle noise smoothing using wavelet transform techniques is presented. Recursive wavelet transforms are used to gradually suppress speckle noise. It is found that this algorithm is more powerful compared to other existing filtering algorithms in terms of speckle suppression for synthetic aperture radar images. Examples show that the ratio of the original standard deviation to mean of about 0.30 (equivalent to 3-look images) can be reduced to 0.05-0.03 (equivalent to more than 100-look images), with a possible small sacrifice of losing some details and narrow edges.

Assessment of orthoimage and DEM derived from ZY-3 stereo image in Northeastern China

ZiYuan-3 (ZY-3, meaning Resource-3) is Chinas first civilian multispectral satellite with high-resolution stereo mapping capability. The along-track stereo images of ZY-3 allow the generation of digital elevation models (DEMs) for various mapping applications. This article evaluated the precision of the derived stereo DEM and orthoimages of ZY-3 data for a test site in Northeastern China. Pixel offset and GPS survey data were used to evaluate the image products. Orthoimages were derived by incorporating rational polynomial coefficients (RPCs) of the satellite orbits and the reference DEMs, including the Advanced Spaceborne Thermal Emission and Reflection Radiomete (ASTER) global digital elevation model (GDEM) and ZY-3 stereo elevation model. The generations of orthoimages were categorised into four approaches depending on the RPCs, control points and/or reference DEMs used. When only the ASTER GDEM was used, the derived orthoimages of the forward and backward viewing sensors showed clear pixel offsets against the GPS check points (CKPs). For example, the offsets of the orthoimage derived using forward-looking image were 13·58 and 26·50 m, in x (easting) and y (northing) directions, respectively. These results also indicated that the pixel offset vectors between the forward and backward orthoimages was systematic which was caused by the error in the RPCs. The second and third approaches were to generate the ZY-3 stereo DEMs first, with and without the use of ground control points (GCPs), and then used the stereo DEMs to generate the orthoimages of the forward and backward looking images. The forth approach used both GCPs and ASTER GDEM to generate the orthoimages. The results showed the use of four GCPs in the process improved the accuracy of the orthoimages. Therefore, ZY-3 can deliver the DEM and orthoimage products to meet the accuracy requirement of the national 1 : 50 000 mapping with four well distributed GCPs.

Accuracy assessment of GDEM, SRTM, and DLR-SRTM in Northeastern China

This paper compares the accuracy of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM), Shuttle Radar Topography Mission (SRTM) C-band and German Aerospace Centre (DLR)-SRTM X-band digital elevation models (DEMs) with the Ziyuan 3 (ZY-3) stereoscopic DEM and ground control points (GCPs). To date, the horizontal error of these DEMs has received little attention in accuracy assessments. Using the ZY-3 DEM as reference, this study examines (1) the horizontal offset between the three DEMs and the reference DEM using the normalised cross-correlation method, (2) the vertical accuracy of those DEMs using kinematic GPS data and (3) the relationship between the three DEMs and the reference ZY-3 DEM. The results show that the SRTM and DLR-SRTM have greater vertical accuracy after applying horizontal offset correction, whereas the vertical accuracy of the ASTER GDEM is less than the other two DEMs. These methods and results can be useful for researchers who use DEMs for various applications.

A model of volume attenuation and backscattering by foliage at L- and P-bands

Abstract In accordance with the distorted Born approximation, a wave approach is developed for the volume attenuation and backscattering coefficients associated with the foliage layer in forests at L- and P-bands. Since the foliage layer is not the dominant layer in forest modelling at longer wavelengths, the orientations of scatterers are assumed to be uniformly distributed. As a result, the ensemble average electric polarizability of scatterers becomes isotropic, generating both volume attenuation and backscattering independent of polarization. It is shown that multiple scattering efTects due to both near and far scatterers are insignificant. It is demonstrated that the total leaf biomass, the mean leaf volume, leaf shape and the dielectric constant are key parameters for the model.