JERS-1 External Calibration Experiments.

Our calibration experiments with JERS-1 cover the determination of the inflight antenna pattern using ground calibration receivers and absolute radiometric calibration using external reference targets. The equipment available comprises 20 L-Band receivers, 5 L-Band transponders and 6 corner reflectors of 3 m leg length. After first tests of the devices we performed measurements on the antenna pattern in March and April 1993. In this paper a detailed description of our experiments and preliminary results are being presented

Calibration of DLR's Experimental Airborne SAR System E-SAR.

Operational calibration of E-SAR requires both external calibration and internal monitoring of the sensor including a recording of instabilities of the transmit power or the receiver gain. Extensive measurements of the receiver gain curve for different settings of the automatic gain control (AGC) have been performed in the laboratory. The output power is being controlled even during data takes using power sensors at the antenna input. For the purpose of external calibration we deploy trihedral corner reflectors in the area surrounding DLR and image these targets at the beginning and the end of each campaign. The analysis of the corresponding image data allows to derive the absolute calibration factor and gives an estimate of the remaining error in radiometric corrections

An Examination of the Assumptions in the Polcal Cross-Talk Removal Algorithm.

JPL's calibration software package POLCAL has implemented the cross-talk removal algorithm presented, which is based on the statistical properties of the image background and does not need any corner reflector or active radar calibrator deployed in the scene. The great advantage of being able to remove the cross-talk contamination without using external calibration targets gives rise to consider algorithms based on clutter statistics in polarimetric SAR images in more detail

Microwave Remote Sensing for Monitoring Forest Vitality.

Reduced forest tree vitality and reduced canopy biomass are often a consequence of disadvantageous stand conditions like lack of water supply and low nutrient availability in the soil. We assume that a direct relationship exists between the stand vitality and the variations of the tree water status and the canopy density. Based on these relations we are investigating the relationship between forest vitality and radar backscatter by combining ground truth measurements, radar signatures from various airborne and spaceborne sensors and model calculations

An Examination of the Assumptions in the POLCAL Cross-Talk Removal Algorithm.

JPL's calibration software package POLCAL has implemented the cross-talk removal algorithm presented in (1), which is based on the statistical properties of the image background and does not need any corner reflector or active radar calibrator deployed in the scene. The great advantage of being able to remove the cross-talk contamination without using external calibration targets gives rise to consider algorithms based on clutter statistics in polarimetric SAR images in more detail

Forest Monitoring with SIR-C/X-SAR.

Two forests - a beech and a spruce stand - were under investigation during the SIR-C/X-SAR missions in April and October 1994. Methodology, ground truth sampling, measurements of dielectric constants, results of attenuation measurements, comparison with modeling (MIMICS) and SAR image analysis were presented

Comparative Investigation of Different Methods for Measuring Dielectric Constants of Tree Constituents.

The dielectric constant is an important input parameter for forest radar backscatter models. Existing methods for measuring dielectric constants can be separated into two major categories: direct, using special RF probes; indirect, measuring the water content and using semiempirical relationships. This paper presents a comparison of the different methods and a detailed accuracy analysis

Topographic Mapping Using a Monopulse SAR System.

We propose a novel design of a SAR system which exploits the monopulse principle to determine the elevation angle and thus the height at the different parts of the image. In this paper, we present design considerations for a corresponding airborne SAR system in X-band and give estimates of the error due to system noise and azimuth ambiguities as well as the expected performance and precision in topographic mapping

Multifrequency and Polarimetric Analysis of Forests in SIR-C SAR Data.

In April and October 1994 the Space Shuttle Endeavour flew the SIR-C/X-SAR missions, where the Earth was observed for the first time with three radar frequencies from space - polarimetric L- and C-band and vertrical polarized X-band. During the two missions extensive ground truth campaigns took place at the Oberpfaffenhofen super test site, where mature, homogeneous and even aged forest stands of Norway spruce (Picea abies) and European beech (Fagus silvatica) on flat terrain were under investigation

Monitoring Central European Forests Using SIR-C/X-SAR Data.

During the two SIR-C/X-SAR missions two deciduous and coniferous forests were observed in the area of Oberpfaffenhofen. First steps toretrieve bio-physical information about these forests from multifrequency and polarimetric data are presented. Starting with the description of the test sites and the collected ground truth data, the paper mainly deals with the results of attenuation measurements, model calculations (MIMICS) and SAR data analysis