Soil Parameter Estimation and Analysis of Bistatic Scattering X-Band Controlled Measurements

To date only very few bistatic measurements (airborne or in controlled laboratories) have been reported. Therefore most of the current remote sensing methods are still focused on monostatic (backscatter) measurements. These methods, based on theoretical, empirical or semi-empirical models, enable the estimation of soil roughness and the soil humidity (dielectric constant). For the bistatic case only theoretical methods have been developed and tested with monostatic data. Hence, there still remains a vital need to gain of experience and knowledge about bistatic methods and data. The main purpose of this paper is to estimate the soil moisture and the soil roughness by using full polarimetric bistatic measurements. In the experimental part, bistatic X-band measurements, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute, will be presented. The bistatic measurement sets are composed of soils with different statistical roughness and different moistures controlled by a TDR (Time Domain Reflectivity) system. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, the sensitivities of the bistatic surface scattering to soil moisture and surface roughness will be discussed. Then, the validation of the specular algorithm by estimating the soil moisture of two surfaces with different roughness scales will be reported. Additionally, a new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness will be presented, as well as evaluation of the sensitivity of phase and reflectivity with regard to moisture variation in the specular direction

System Concepts for Bi- and Multi-Static SAR Missions

The performance and capabilities of bi- and multistatic spaceborne synthetic aperture radar (SAR) are analyzed. Such systems can be optimized for a broad range of applications like frequent monitoring, wide swath imaging, single-pass cross-track interferometry, along-track interferometry, resolution enhancement or radar tomography. Further potentials arises from digital beamforming on receive, which allows to gather additional information about the direction of the scattered radar echoes. This directional information can be used to suppress interferences, to improve geometric and radiometric resolution, or to increase the unambiguous swath width. Furthermore, a coherent combination of multiple receiver signals will allow for a suppression of azimuth ambiguities. For this, a reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of non-optimum receiver aperture displacements leading to a non-uniform sampling of the SAR signal. This algorithm has also a great potential for systems relying on the displaced phase center (DPC) technique, like the high resolution wide swath (HRWS) SAR or the split antenna approach in the TerraSAR-X and Radarsat II satellites

A SAR conjugate mirror

A radar transponder was constructed, which modifies the received signal such that its complex conjugate is returned to the radar, qualities of the conjugate mirror used in optics and acoustics. For a monostatic synthetic aperture radar (SAR), a perfect conjugate mirror will reflect a signal back to the radar with no phase shift due to the propagation path. The signal received by the transponder is also decorrelated from other targets, enhancing the transponder signal in the SAR image. This letter describes a transponder operated as a SAR conjugate mirror and an experiment with the European Remote Sensing 1 satellite, demonstrating the feasibility and characteristics. The significance for transponder design is addressed and possible applications discussed

A Passive Multistatic CW Radar System using Geostationary Illuminators

In this paper a new passive radar system using a geostationary TV satellite as an illuminator and ground-based receivers is presented. The system can be operated as a monostatic or multistatic radar and can be used for target detection or reflectivity measurements. Full polarimetric operation is possible. The measurement technique and the system hardware of an experimental system are described, particular attention being paid to the methods of signal synchronization. The results of experiments with the radar are presented and future developments dis-cussed

A Tandem TerraSAR-X Configuration for Single-Pass SAR Interferometry

TanDEM-X is a mission proposal for a TerraSAR-X add-on satellite to enable high-resolution single-pass SAR interferometry. The TanDEM-X mission has the goal of generating a global Digital Elevation Model (DEM) with an accuracy corresponding to the DTED-3 specifications (12 m posting, 2 m relative height accuracy for flat terrain). This paper describes the mission concept and requirements, including several innovative aspects like operational modes, orbit selection and maintenance as well as PRF and phase synchronization. Results from a performance estimation show the achievable DEM accuracy. Finally, an overview of the potential of the TanDEM-X mission for several scientific applications is presented

The Shuttle Radar Topography Mission (SRTM)

INTRODUCTION More than 1800 years after Claudius Ptolemy wrote his books Amalgest and Geographike Sytaxis laying down the foundations of astronomy and geography for centuries to come. Modern manifestations of his theories - orbiting satellites carrying remote sensing instruments to image the Earth's surface - are culminating in a mission to survey the Earth from space. Ptolemy's map of the known world was still in use 1100 years later. He would have been impressed with the SRTM mission which will survey the earth in just ten days. The Shuttle Radar Topography Mission (SRTM) will achieve in a single shuttle flight what an army of surveyors couldn't achieve in a lifetime: to survey the land masses between 60 North and 58 South. The SRTM mission will generate consistent, comprehensive topographic data and radar images to model the terrain and map the land of most of the inhabited surface of the Earth. The instrument used is a Synthetic Aperture Rad

Surface Parameter Estimation using bistatic polarimetric X-band Measurements

The main purpose of this paper is to separately estimate the important surface parameters (soil moisture and roughness) by using full polarimetric bistatic measurements. The results provide a basis for new satellite application of future bistatic measurement systems such as the TanDEM-X satellite mission. Initially, bistatic X-band measurements, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute, will be presented. The bistatic measurement sets are composed of soils with different well-known statistical roughness scales and different moistures. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, the assessment of the surface parameters (soil moisture and surface roughness) using the well calibrated data introduced in the former related part, will be detailed. The validation of the specular algorithm by estimating the soil moisture of two surfaces with different roughness scales will be reported. Additionally, a new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness will be presented, as well as the sensitivity of phase and reflectivity with regard to moisture variation and therefore the penetration depth was evaluated. Current results demonstrate a non-linear relationship between the signal phase and the soil moisture, as expected, confirming the possibility of using DInSAR to measure variations in soil moisture

TerraSAR-X CALIBRATION PLAN

As TerraSAR-X will be an operational scientific as well as commercial mission, product quality will be of paramount importance. Together with service reliability it is essentially dependent on the calibration and the performance verification of the radar system. The present document describes a detailed plan to calibrate the TerraSAR-X instrument system. This Terra-SAR-X calibration plan is based on the well established methodology developed for ERS-1, SIR-C/X-SAR, SRTM and ENVISAT/ASAR

Feasibility of a Spaceborne P-Band SAR for Land Surface Imaging

The use of VHF wavelengths, e.g. P-Band, for imaging land surface features is a promising method of environmental monitoring. However, at these wavelengths propagation, interference from other services and antenna technology are a challenge. The paper discusses the uses and the technical feasibilty of a spaceborne instrument