Advanced Technique, 1992-1994

Steps have been taken to improve the second geophysical environmental research cooperation (GER II) airborne imaging spectrometer (IS) to the European airborne remote sensing capability (EARSEC) system. The first two flights have taken place with the main purpose of debugging. The airborne optical system calibration laboratory was set up and calibration procedures agreed. Considerable effort was devoted to the development of the EARSEC optical sensor processor system. The first phase of the EARSEC synthetic aperture radar (SAR) processor development was completed and the final requirements and design of the processor were reviewed and approved. The development phase was scheduled and the first prototype version was installed. The prototype version is coded in a computing environment for high performance numeric computation and visualization (Matlab). Data sets acquired in the European microwave signature laboratory (EMSL) and simulated data were used for the testing of the algorithms in the Matlab environment prior to the integration of the modules in the C++ operational version of the system.

A European microwave signature laboratory (EMSL) has been established. The first experiments were carried out on different types of metallic and dielectric targets. They were aimed at the validation of theoretical models and at understanding of the dominant scattering mechanisms in relatively simple targets. Next, several types of extended targets were measured by using a linear displacement of the scene with respect to the sensor to simulate the operation of air space borne synthetic aperture radar (SAR) sensors. The excellent results obtained alter processing confirmed the high quality of the microwave measurements and the accuracy of the mechanical movements. Time was devoted to the construction of special target adapters and the acquisition of instrumentation for measuring soil moisture and surface roughness in preparation for future experiments. 3 major upgrades were carried out during 1993. The microwave measurement system was upgraded to increase the measurement speed. A monitoring system was installed, giving complete representation on a monitoring screen of control and environmental parameters. A video grabber was installed to digitize the video signals from the cameras installed on sleds beside the sensors. Several study contract were placed in relation to the activity of the EMSL with outside companies and institutions. The analysis of the data on the EMSL quiet zone test has led to an initial characterization of the spatial antenna response of the sensors. Further analysis has been undertaken on the polarimetric characteristics of the antennae. Among the data acquired on several types of objects, a detailed analysis has been undertaken for collections of dielectrical cylinders and sections of tree branches. Following preliminary assessment of the compatibility of the laboratory data with an operational SAR processor, the first interferogram was produced using two SAR images taken over a flat gravel surface. Several 2-dimensional imaging experiments were undertaken to compare different types of processing methods and using both the linear and the rotational target motion.

High resolution spectral measurements have been carried out on selected vegetation types with different biochemical content to study the optical properties and to establish a spectral signature database. 120 samples were collected, representative of both agricultural and nonagricultural vegetation types. Spectral reflectance and transmittance measurements were performed on single and stacked leaves. The samples were then dried and the spectral measurements were performed again. The dried samples were then sent for chemical analysis to 2 different laboratories. The results of the first series of analysis concerned the relative concentration of biochemical components such as lignin, cellulose, starch, water and nitrogen. This is one of the most comprehensive data sets which has ever been established for remote sensing purposes involving the spectral properties of vegetation and its biochemical components. First comparisons of the spectral signatures with the chemical analyses show some promising correlations especially with the spectral measurements made on dry samples. A new European goniometric facility has been installed and tested. This instrument allows a light source and a detector to be independently positioned anywhere on a 2 m radius hemisphere centred on the target and thereby to perform bidirectional measurements. The control software allows the full programming of an experiment, the graphical visualization of the geometry and the interface to a dedicated data base for the experimental results. A 2 stream radiative transfer model has been developed to investigate different absorption features in the reflectance spectrum of leaves and canopies. The investigation was focussed in the spectral window of 1.65 to 1.76 um thought to be a signature of lignin. It was concluded that the 1.7 um residual does show a systematic relation with the vegetation cover type.

Techniques for information extraction from radar signals have been assessed in view of remote sensing applications in forestry and land use. Several important directions were pursued including: basic interferometric techniques; advanced interferometric techniques for the extraction of geophysical parameters in forestry applications; experimental characterization of synthetic aperture radar (SAR) spatial statistics as a function of several parameters, in particular study of the dependency on polarization and introduction of the concept of polarimetric texture signature; modelling and experimental characterization of terrain relief effects on the polarimetric radar signal; study of the dielectric properties of complex targets, from the microscopic physics point of view, and from the macroscopic scattering theory. Much effort has been devoted to the development of SAR techniques in remote sensing applications projects including: preprocessing using a speckle filter and averager, classified and georeferencing geocoding packages; Gamma Gamma MAP filtering, averaging, automatic edge detection, single date classification, multitemporal classification; a study on the phenological interpretation of changes in radar backscattering. An investigation was started to develop a technique based on multipass SAR interferometry to extract biophysical information about the temperate forest. The interferometric technique provides high resolution topographic data, which are useful for calibration and direct measurement of tree height, and yield information on the 3-dimensional structure of the canopy. These cannot be measured by any other remote sensing technique. Results achieved include: review of literature on scattering models; development of improved algorithms to generate height maps from earth remote sensing satellite number 1 (ERS-1) interferometric data sets; development of algorithms and software to generate slopes maps; validation of the algorithms using ERS-1 data sets.