The European Microwave Signature Laboratory (EMSL), recently built at the Joint Research Center of the Commission of European Communities (CEC) at Ispra, is a state-of-the-art experimental facility which provides unique opportunities in terms of measurement capabilities and data processing. The laboratory is mainly devoted to polarimetric radar measurements aimed to complement air- and spaceborne remote sensing experiments by providing stable and reproducible environmental conditions and flexible operational modes for well-controlled experiments. As one of the European Large Facilities, the EMSL is open to collaboration with all interested research groups both within the European Union and outside. The EMSL anechoic chamber has an hemispherical shape with a diameter of 20 m and hosts two independently movable TX/RX modules plus a set of fixed receiving antennae. A positioner with linear and rotary movements is used to transport and accurately move the target under test inside the chamber. The selection of different geometrical configurations (mono-, bi-, multi-static) and measurement modes (scatterometric, 2D and 3D imaging) is made possible by this special architecture of the facility. In this paper, first a description of the main components of the laboratory is given, then the performances of the measurement system are discussed on the basis of the results of verification tests (Stability, Sensitivity, Antenna pattern characterization) and finally a selection is presented of the most significant outcomes of the experiments undertaken until now.

A significant experiment for evaluating the potential of Synthetic Aperture Radar (SAR) in monitoring soil and vegetation parameters is being carried out on an agricultural area located in Central Italy. The site has been imaged in 1991 by NASA/JPL AIRSAR during the MAC-91 Campaign and subsequently by ESA/ERS-1 and NASDA JERS-1 in 1992. The sensitivity to vegetation biomass of backscattering coefficient measured by ERS-1 and JERS-1 radars is discussed and compared with the best results achieved using the multifrequency polarimetric AIRSAR data.

In order to assess the actual industrial potential and limitations of SAR interferometry to generate DEM, we have processed several interferometric data and generated several DEM over different regions. In this paper we present several ERS-1 interferograms and interferometric DEM on mountainous, hilly and flat areas. The interferograms have been generated by CNES and we performed the unwrapping and geometric processing in order to get the final cartographic product. This processing chain is described. According to the different geometric and radiometric parameters such as the baseline and the nature of the coverage over each of these regions, we discuss the achieved or achievable final DEM accuracy, the incoherences, the artefacts level as well as the different steps along the processing chain. We describe the actual results compared to SPOT and/or USGS DEMs. The need for the three components of the interferometric products generated by CNES (Amplitude image, Coherence image and Phase difference image) will be demonstrated. Finally we will draw some conclusions in terms of operational accuracies and limitations.

An airborne system comprising four SARs that operate in the C - ((lambda) approximately equals 4 cm), L - ((lambda) approximately equals 23 cm), P - ((lambda) approximately equals 68 cm) and VHF - ((lambda) approximately equals 250 cm) - bands is presented. A general description of each SAR is given together with its basic performance characteristics. Design peculiarities of transmit- receive channels, antenna units, radar data recorders and digital data processing algorithms are discussed. Terrain radar images obtained with the use of SARs operating at different wavebands with various polarizations are presented.

In this paper a new real-time flood monitoring system using SAR is described. Flooding has been a puzzling problem to the Chinese government for a long time. During the last decade, China promoted a research program of flood monitoring and management using remote sensing techniques and established a quasi-real-time and real-time disaster monitoring system. The system has two functions: flood monitoring by SAR and an image transmitting system, and loss estimation of flooded area using an image processing GIS system. This system was used successfully in the 1991 flood in China and played an important role in reducing flood losses. To establish this system several key technical problems were solved, including the SAR system, SAR image processing, SAR image compression, and image long distance communication and information system.

The U.K. Meteorological Office (UKMO) is providing to NOAA three flight models of the high frequency part of the Advanced Microwave Sounding Unit known as AMSU-B. The AMSU-B is a five channel microwave radiometer with channels centered at 89, 150, 183+/- 1, 183+/- 3 and 183+/- 7 GHz with a field of view of nominally 1.1 degree(s) (i.e. 15 km footprint at nadir). AMSU-B will fly on the NOAA KLM polar orbiters due to be launched in the next few years. All three AMSU-B flight models have undergone a comprehensive test and characterization program to measure the antenna pattern and spectral, radiometric and thermal properties of each instrument. The results from this test program have allowed a procedure for the in-orbit calibration of AMSU-B to be defined. In parallel with the development of the AMSU-B radiometer a program of aircraft radiometer measurements and model development has been carried out with the aim of improving our capability of predicting the radiative transfer through the atmosphere at AMSU-B frequencies. The aircraft radiometer has channels at 89 GHz and 157 GHz which are close to the corresponding window channels of AMSU-B and it can view both upwards and downwards. Measurements of clear transmission, sea surface emissivity and transmission through cloud liquid water have all been analyzed. Based on these measurements a forward radiative transfer model is being developed which will be used in the retrieval of temperature, humidity and cloud liquid water from AMSU.

A microwave radiometer relies on the power linearity of its microwave receivers to accurately measure the temperature of remote microwave noise sources. This paper considers linearity issues in the design and characterization of such receivers. Analysis is presented relating the radiometer temperature interpolation error to a second order power nonlinearity coefficient for the receiver. Formulas are also developed specifying the temperature error in terms of individual receiver component parameters. It is shown that the key parameter for the RF detector in the receiver is A₄, a fourth order RF distortion coefficient, and the key parameter for the RF amplifiers in the receiver is IP₃, the third order intercept. This paper also discusses experimental methods for measuring the power linearity of RF detectors to the levels required for radiometric applications. Three methods are discussed: the two-tone method, the amplitude modulation method, and the constant ratio method. The theory of determining the coefficients that characterize the nonlinearity of the detector from experimental data is presented. Experimental results are presented showing that the two-tone method and the constant ratio method agree to within experimental error. The sensitivity for measuring nonlinearities and the difficulties encountered in implementing each of these methods are also discussed.

The Tropical Rainfall Measurement Mission (TRMM) satellite will carry with it a microwave radiometer called TRMM Microwave Imager (TMI). It is a five frequency, nine channel conical scanning microwave radiometer, operating at the frequencies of 10.65, 19.35, 21.3, 37.0, and 85.5 GHz. Each frequencies has both vertical and horizontal polarizations, except the 21.3 GHz channel, which has vertical polarization only. The TMI and a companion Precipitation Radar (PR) will provide the primary rainfall measurement capability of TRMM. A description of the TMI instrument will be given, its design features, mode of operation, and projected performance will be discussed.

Microwave emission of the Earth's surface is the fundamental process exploited by passive microwave sensors to detect land and ocean signatures. In land applications microwave radiometers have a high sensitivity to water content of soil, vegetation and atmosphere, and their use can be of great interest in hydrology, meteorology, climatology and in agriculture as well. This paper is a report on research currently in progress which intends to investigate the capability of microwave data from spaceborne sensors in the monitoring of some land surface parameters in the European landscape, where spatial and temporal variations are very high and the climatic conditions change from very dry and hot regions to humid, cold and rainy areas. The objective is to extend on a larger scale certain relations between microwave emission and land parameters which have been established theoretically and in many experiments with ground based and airborne sensors.

A major application for a 21 cm radiometer is the remote sensing of soil moisture which is possible because of the large contrast between the dielectric constant of dry soil (approximately equals 3.5) and that of liquid water ( approximately equals 80). One of the major problems with the utilization of long wavelength radiometers from satellite platforms has been the large antenna size required with its substantial mass. For example, at satellite altitudes an antenna size of at least 10 m is required to obtain resolutions in the 10-20 km range. The size requirement is fundamental but the mass can be reduced by using unfilled arrays or as will be described here a thinned array antenna. Such a system operating at L-Band ((lambda) equals 21 cm or 1.42 GHz) has been developed and tested from an aircraft platform. It is called ESTAR (Electronically Scanned Thinned Array Radiometer) and it uses linear (stick) antennas in the along-track direction and aperture synthesis between pairs of sticks separated by odd multiples on half wavelengths in the cross track direction. The approximate dimensions of the antenna are 1 meter by 1 meter. Results from an evaluation series of flights over a study watershed in Oklahoma indicate that such a system can provide useful soil moisture information.

The passive microwave radiometers have a field of view that is much larger than the size of the raining cells, and within the rain cell the brightness temperature can reach saturation. These problems are generally referred to as the beam filling effect (BFE). We developed a technique to retrieve rain rates from the Special Sensor Microwave/Imager (SSM/I) data, which inherently incorporates the BFE. However an overestimation of rain rates was evident when the data from the Global Precipitation Climatology Project (GPCP) program became available. The procedure followed to obtain the algorithm was revised and modified, and new coefficients were calculated. This modified algorithm was tested by comparing the SSM/I derived rainfall with the corresponding values obtained by radar and rain gauges in the framework of the GPCP program. This comparison reveals two separate clusters of points, which can be related to the fact that the BFE is larger for convective precipitating clouds and smaller for stratiform clouds. An examination of the data at 19 and 85 GHz gives a clue to discriminate between these two types of rain. Then two different algorithms are proposed for the retrieval of rain from microwave data.

A multichannel scanning microwave spaceborne radiometer is described designed to sea ice monitoring, natural resources studied, ocean and atmosphere research and monitoring. The radiometer operates at the following wavebands: 0.4 cm, 0.8 cm, 1.35 cm, 2.0 cm and 5.5 cm. In the 0.4 cm waveband it receives radiation with only one polarization (either horizontal or vertical). In other wavebands it can receive vertically and horizontally polarized signals simultaneously. Precise polarization measurements are performed with the help of a scanning antenna system of a special design allowing to receive radiations at all the wavebands and polarization at exactly the same viewing angle with high polarization isolation. A mode when the forward and the backward survey lines are received simultaneously is provided. In addition, all the channels can be completely calibrated against both 'the absolute black body' and the open space. Digital signal processing is performed on board the satellite until absolute radiobrightness temperature values and images with rectified lines are obtained. Output data is presented in the form suitable for its reception and display at the available and widely used receiver stations.

The Greenland Sea is a sub-arctic sea that links the Arctic Ocean to the Atlantic Ocean by way of the East Greenland Current that originates in the Arctic Ocean and follows largely the break of the continental shelf from Fram Strait to Denmark Strait. The Greenland Sea encompasses the special phenomenon described as the Bukta-Odden phenomenon of rapid changes of ice concentration along the shelf break, and deep-water formation. Also, it shows examples of the formation of polynyas along the coast including the North-East Water polynya at the northeast coast of Greenland. Studies of the Greenland Sea are carried out by use of Earth observation satellite data. Research issues are discussed with examples of observations by visual/infrared and passive and active microwave instruments. A great deal of work is carried out with development of procedures for analysis of data from ice-frequented waters including combination of visual/infrared data with active and passive microwave data to improve monitoring of the area in question. With the ice used as a tracer, information is obtained about the dynamics of the area as a result of ocean current and wind.

MIMR (Multifrequency Imaging Microwave Radiometer) is an instrument under development for the European Space Agency (ESA) by the European Industry, with Alenia Spazio as Prime Contractor. It is a conical scanning passive microwave radiometer, which shall measure the Earth surface brightness temperature by processing the received electro- magnetic Earth surface radiation in linear polarization. Its output products will be of prime importance for monitoring of the environment, and will provide useful data for climatology and meteorology with day and night operation capabilities and near global daily coverage. The experience gained through various programs since 1972 with NIMBUS satellite's series utilizing ESMR, NEMS, SCAMS, SMMR instruments and DMSP-Block 5D-2 satellite with on-board SSM/I instrument led to the MIMR concept with better performance than the instruments already flown. MIMR has successfully passed a design phase, which has established an instrument baseline suited for accommodation on either the NASA EOS or ESA METOP spacecrafts, and a breadboarding activity devoted to key items. A Demonstrator model of the Instrument is currently under development, which shall prove by test its challenging performance: it will be representative of the flight design, performing measurements at 6.8, 36.5 and 89.0 GHz. Within this paper emphasis will be put on the receivers key design topics, as driven by performance and technology trade-offs, with an overview of the achieved performance in the frame of development activity.

The determination of the optimum experimental conditions to produce the best qualitative results is necessary both in active and passive microwave remote sensing (RS). In this paper we show the decision process involved in solving two problems connected with the selection of the best conditions for earth surface microwave RS: Calculation of the statistical relationship between scattered and proper surface radiation data for different kinds of surface sensed. Determination of the optimal algorithms and boundary accuracies for surface parameters by active and passive microwave sensors. Optimal estimation algorithms for surface parameters (dielectric permittivity, thermodynamical temperature, surface slop, spectral spatial components of rough surface height, etc.) have been found by a maximum likelihood function method. The results found can help to plan RS microwave experiments of surface parameter estimation with predicted accuracies.

A new microwave sensor in which active and passive mode sensors are working synergistically is designed for future China space projects. In the system the scatterometry, altimetry and radiometry functions are integrated technically. There are three operation modes and the mode combination can be selected in order of user requirement. The main modes are: ALT + RAD1, SCAT + RAD1, Multifrequency RAD, working at five frequency band (RAD2 - RAD6). Altimeter, Scatterometer and Radiometer RAD1, working at same ku band frequency and use a common antenna. The system design is based at operational airborne sensors which was in operation from early 1980. Main key problem of the system is solving during the design of this system is the mode combination technique, antenna technology, data management and system calibration.

The term 'multispectral' is used to describe imagery with anywhere from three to about 20 bands of data. The images acquired by Landsat and similar earth sensing satellites including the French Spot platform are typical examples of multispectral data sets. Applications range from crop observation and yield estimation, to forestry, to sensing of the environment. The wave bands typically range from the visible to thermal infrared and are fractions of a micron wide. They may or may not be contiguous. Thus each pixel will have several spectral intensities associated with it but detailed spectra are not obtained. The term 'hyperspectral' is typically used for spectral data encompassing hundreds of samples of a spectrum. Hyperspectral, electro-optical sensors typically operate in the visible and near infrared bands. Their characteristic property is the ability to resolve a large number (typically hundreds) of contiguous spectral bands, thus producing a detailed profile of the electromagnetic spectrum. Like multispectral sensors, recently developed hyperspectral sensors are often also imaging sensors, measuring spectral over a two dimensional spatial array of picture elements of pixels. The resulting data is thus inherently three dimensional - an array of samples in which two dimensions correspond to spatial position and the third to wavelength. The data sets, commonly referred to as image cubes or datacubes (although technically they are often rectangular solids), are very rich in information but quickly become unwieldy in size, generating formidable torrents of data. Both spaceborne and airborne hyperspectral cameras exist and are in use today. The data is unique in its ability to provide high spatial and spectral resolution simultaneously, and shows great promise in both military and civilian applications. A data analysis system has been built at TRW under a series of Internal Research and Development projects. This development has been prompted by the business opportunities, by the series of instruments built here and by the availability of data from other instruments. The products of the processing system has been used to process data produced by TRW sensors and other instruments. Figure 1 provides an overview of the TRW hyperspectral collection, data handling and exploitation capability. The Analysis and Exploitation functions deal with the digitized image cubes. The analysis system was designed to handle various types of data but the emphasis was on the data acquired by the TRW instruments.

The results of orbit parameters calculations for satellites METEOR-2/20, 2/21 (h equals 950 km) and METEOR-3/5, 3/7 (h equals 1200 km) are analyzed. The accuracy of orbit approximation and extrapolation (prediction) for different initial data assimilation techniques is evaluated using analytical navigation model. Mean 14 day orbit prediction error during 1991-1994 amounted to 9.5 km for METEOR-2/20 and 5.6 km for METEOR-3/5. The same value for METEOR-2/21 (start 31 Aug 1993) was 2.9 km, for METEOR-3/7 (start 25 Jan 1994) was 1.3 km. The accuracy of satellite orbit prediction as well as orbit approximation is changing for the worse under high solar activity conditions. The estimates of real pixel location and estimates of deflections of axes positions for IR- radiometers << Klimat >> (10.5-12.0 mkm, 12 X 12 km²) of METEOR-3/5 and 3/7 and ScaRaBlaunched on METEOR-3/7 for Earth radiation budget measurements have been obtained. No essential systematic axes deflections and pixel location errors were detected except systematic roll angle bias of -29' for << Klimat >> on METEOR-3/5. Estimates of ground control points positions using MWDB-II database demonstrate pixel location accuracy of about 0.5 pixel size.

Multitemporal spaceborne and aerial image data as well as cartographic and historical materials about Franz Josef Land archipelago published since 1874 were acquired and jointly analyzed. Complex of photogrammetric and cartographic investigations was carried out being based on remote sensing data and supported by field direct measurements in test areas. Three-dimensional terrain models and large-scale basic maps were created by means of digital photogrammetry, stereoplotting and image interpretation. Achieved and expected accuracies were discussed. Moreover, present state and dynamics of glaciation of Franz Josef Land were evaluated and argued recommendations were given to select to preferable areas and periods of further terrestrial explorations. Results were integrated in thematic (topographic, glaciological) information system.

This paper presents a fully digital photogrammetric method for the restitution of various types of stereo imagery (visible and SAR; spaceborne and airborne) using the same digital stereo workstation, the DVP. Based on personal computer, the DVP system enables the on-line three dimensional reconstruction of a stereo-model, the capture in real time of data from the raw images and the graphic overlay of vector data. The mathematical equations, which drive the DVP, are based on the collinearity and co-planarity conditions and integrate the platform, sensor, Earth and cartographic projection models into a single model. Data is extracted using the DVP system and compared to digital topographic data. Three different challenging study sites and data sets have been selected to test the limits of the method and the DVP system. Planimetric accuracies of 6.5 m, 30.0 m and 17.0 m, and altimetric accuracies of 12.6 m, 38.0 m and 23.9 m have been achieved with SPOT-P, airborne SAR and ERS-SAR stereo-pairs, respectively. Better results should be achievable with less challenging study sites and data sets.

Operationalization has been a major concern in the remote sensing and cartography communities for years. The presented system SAT-GIS is a big step forward towards operational satellite image interpretation and digital cartography in an integrated GIS environment. The SAT-GIS development followed two major objectives (1) to provide a common graphical user interface (GUI) in order to fully integrate the worlds of raster, vector and attribute data processing and (2) to automate complex workflows with a maximum of interactive support. As a result, SAT-GIS provides to the user the necessary means to most efficiently perform his work in an intuitive manner. Facing budgetary limits and quite a short period of time for the development, SAT-GIS has been implemented with an utmost use of existing commercial software packages and easy-to-use development tool-kits. This paper describes the characteristics of SAT- GIS, its field of application, the development and highlights of those development activities which yielded the unique system capabilities of SAT-GIS.