TerraSAR-X is Germany's new radar remote sensing flagship. It carries an advanced high-resolution X-band SAR
instrument. The key element of the system is the active phased array antenna nominally operated with a bandwidth of
100 MHz or 150 MHz and an experimental 300 MHz capability. The instrument's flexibility with respect to electronic
beam steering and pulse-to-pulse polarization switching allows the acquisition of SAR data in Stripmap, Spotlight and
ScanSAR imaging configurations in different polarization modes for a wide range of incidence angles.
The mission is implemented in the framework of a public-private partnership between the German Aerospace Center
(DLR) and EADS Astrium GmbH Germany and will provide high resolution SAR data products for commercial use and
Processing of the payload data will be performed at DLR's Payload Ground Segment (PGS) for TerraSAR-X. The
central part of PGS is the TerraSAR Multi-Mode SAR Processor (TMSP) focusing the SAR data in a unified way for the
different imaging configurations. A wide range of processing options spanning from phase preserving complex products
in slant range geometry to orthorectified terrain corrected intensity images lead to a comprehensive collection of SAR
product types and variants. During the 5 months lasting commissioning phase the complete processing chain will be
properly tuned and adjusted. The TMSP algorithms have to be configured, e.g. thresholds for calibration pulse analysis,
estimation window sizes for SAR data analysis, parameterization of estimation algorithms. Also the configuration of
product variants with respect to resolution and radiometric quality will be checked and refined.
This paper shortly reviews the different imaging configurations and product variants and gives a report on the SAR
processor checkout activities and presents the first results.
At the German Aerospace Center, DLR, an automatic and operational traffic processor for the TerraSAR-X ground segment is currently under development. The processor comprises the detection of moving objects on ground, their correct assignment to the road network, and the estimation of their velocities. Since traffic flow parameters are required for describing dynamics and efficiency of transportation, the estimation of the velocity of detected ground moving vehicles is an important task in traffic research science. In this paper we show for TerraSAR-X simulated data how the along-track velocity component of a moving vehicle can be derived indirectly by processing SAR data with varying frequency modulation (FM) rates and exploiting the specific behavior of the vehicle's signal through the FM rate space. An airborne ATI-SAR campaign with DLR's ESAR sensor has been conducted in April 2004 in order to investigate the different effects of ground moving objects on SAR data and to acquire a data basis for algorithm development and validation. Several test cars equipped with GPS sensors as well as vehicles of opportunity on motorways with unknown velocities were imaged with the radar under different conditions. To acquire reference data of superior quality, all vehicles were simultaneously imaged by an optical sensor on the same aircraft allowing their velocity estimation from sequences of images. The paper concentrates on the estimation of along-track velocities of moving vehicles from SAR data. Velocity measurements of vehicles in controlled experiments are presented, including data processing, comparison with GPS and optical reference data and error analysis.
Airborne imaging spectrometers have a history of about 20 years starting with the operation of AIS in 1982. During the following years, many other instruments were built and successfully operated, e.g., AVIRIS, CASI, DAIS-7915, and HyMap.
Since imaging spectrometers cover a spectral region with a large number of narrow contiguous bands they are able to retrieve the spectral reflectance signature of the earth allowing tasks such as mineral identification and abundance mapping, monitoring of vegetation properties, and assessment of water constituents. An essential prerequisite for the evaluation of imaging spectrometer data is a stable spectral and radiometric calibration. Although a considerable progress has been achieved in this respect over the last two decades, this issue is still technically challenging today, especially for low-to-medium cost instruments.
This paper introduces a new airborne imaging spectrometer, the ARES (Airborne Reflective Emissive Spectrometer) to be built by Integrated Spectronics, Sydney, Australia, and co-financed by DLR German Aerospace Center and the GFZ GeoResearch Center Potsdam, Germany. The instrument shall feature a high performance over the entire optical wavelength range and will be available to the scientific community from 2006 on. The ARES sensor will provide 150 channels in the solar reflective region (0.47-2.42 μm) and the thermal region (8.1-12.1 μm). It will consist of two co-registered optical systems for the reflective and thermal part of the spectrum. The spectral resolution is intended to be between 12 and 16 nm in the solar wavelength range and should reach 150 nm in the thermal range.
ARES will be used mainly for environmental applications in terrestrial ecosystems. The thematic focus is thought to be on soil sciences, geology, agriculture and forestry. Limnologic applications should be possible but will not play a key role in the thematic applications. For all above mentioned key application scenarios, the spectral response of soils, rocks, and vegetation as well as their mixtures contain the valuable information to be extracted and quantified.
The radiometric requirements for the instrument have been modeled based on realistic application scenarios and account for the most demanding requirements of the three application fields: a spectral bandwidth of 16 nm in the 0.47-1.8 μm region, and 12 nm in the 2.02 - 2.42 μm region. The required noise equivalent radiance is 0.05, 0.03, and 0.02 Wm-2sr-1μm-1 for the spectral regions 0.47- 0.89 μm, 0.89 - 1.8 μm, and 2.02 - 2.42 μm, respectively. In the thermal region similar simulations have been carried out. Results suggest a required noise equivalent temperature of 0.05 K for the retrieval of emissivity spectra in the desired accuracy. Nevertheless, due to system restrictions these requirements might have to be reduced to 0.1 K in the wavelength range between 8.1 and 10 μm and 0.1-0.2 K from 10 to 12.1 μm.
A new airborne imaging spectrometer introduced: the ARES (Airborne Reflective Emissive Spectrometer) to be built by Integrated Spectronics, Sydney, Australia, financed by DLR German Aerospace Center and the GFZ GeoResearch Center Potsdam, Germany, and will be available to the scientific community from 2003/2004 on. The ARES sensor will provide 160 channels in the solar reflective region (0.45-2.45 μm) and the thermal region (8-13 μm). It will consists of two separate coregistered optical systems for the reflective and thermal part of the spectrum. The spectral resolution is intended to be between 12 and 15 nm in the solar wavelength range and should reach 150nm in the thermal. ARES will be used mainly for environmental applications in terrestrial ecosystems. The thematic focus is thought to be on soil sciences, geology, agriculture and forestry. Limnologic applications should be possible but will not play a key role in the thematic applications. For all above mentioned key application scenarios the spectral response of soils, rocks, and vegetation as well as their mixtures contain the valuable information to be extracted and quantified. The radiometric requirements for the instrument have been modelled based on realistic application scenarios and account for the most demanding requirements of the three application fields: a spectral bandwidth of 15 nm in the 0.45-1.8 μm region, and 12 nm in the 2 - 2.45 μm region. The required noise equivalent radiance is 0.005, 0.003, and 0.003 mWcm-2sr-1μm-1 for the spectral regions 0.45-1 μm, 1 - 1.8 μm, and 2 - 2.45 μm, respectively.
This paper reviews the concept of noise in 2D phase unwrapping of SAR interferograms. It is shown that phase gradient estimates derived as wrapped phase differences of adjacent samples are biased, leading to an underestimation of phase slopes. Hence, linear estimators like least squares methods operating on such gradient estimates tend to globally distort the reconstructed terrain. The slope bias is quantified as a function of coherence and number of looks both theoretically and via simulations. The particular type of noise under discussion also may lead to impulse-like errors in the phase unwrapped by a linear method. In order to avoid these errors the support of reconstruction must be restricted in the same way as with so-called branch-cut methods.
An approach to 2D phase unwrapping for SAR interferometry is presented, based on separate steps of coarse phase and fine phase estimation. The coarse phase is constructed from instantaneous frequency estimates obtained using adaptive multiresolution, in which estimation is done of difference frequencies between resolution levels, and the frequency differences are summed over resolution levels such that a conservative phase gradient field is maintained. This allows a smoothed coarse unwrapped phase, which achieves the full terrain height, to be obtained with an unweighted least squares phase construction. The coarse phase is used to remove the bulk of the phase variation of the interferogram, allowing more accurate multilooking, and the resulting fine phase in unwrapped with weighted least squares. The unwrapping approach is verified on simulated interferograms.
Repeat-pass interferometry data have been acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry on four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model has been derived. The limitations of the X-SAR interferometry are discussed.