We report the results of a preparatory study aimed at exploring candidate applications that could benefit from a passive micro-satellite accompanying the L-band SAOCOM-1B satellite of Argentina, and to carry out a limited demonstration, based on data acquired during ESA airborne campaigns, of selected applications. In a first step of the study, the potential applications were identified and prioritized based on the mission context and strategic applications, scientific need, and feasibility. The next step of the study was to carry out some demonstrations using data sets acquired during the BioSAR 2007-2009, TropiSAR 2009 and IceSAR 2007 campaigns. A P-band InSAR digital elevation model was generated from BioSAR 2007 data. Time-series of interferometric coherence maps were obtained as a tool for change detection and monitoring. PolInSAR processing was carried out on BioSAR 2007 and IceSAR data.
Multi-Chromatic Analysis (MCA) of SAR images relays on exploring sub-band images obtained by processing portions
of range spectrum located at different frequency positions. It has been applied to interferometric pairs for phase
uwrapping and height computation. This work investigates two promising applications: the comparison between the
frequency-persistent scatterers (PSfd) and the temporal-persistent scatterers (PS), and the use of inter-band coherence of a single SAR image for vessel detection. The MCA technique introduces the concept of frequency-stable targets, i.e.
objects exhibiting stable radar returns across the frequency domain which is complementary to that of temporal stability
at the base of PS interferometry. Both spotlight and stripmap TerraSAR-X images acquired on the Venice Lagoon have
been processed to identify PSfd and PS. Different populations have been analyzed to evaluate the respective
characteristics and the physical nature of PSfd and PS. Concerning the spectral coherence, it is derived by computing the
coherence between sub-images of a single SAR acquisition. In the presence of a random distribution of surface
scatterers, spectral coherence must be proportional to sub-band intersection of sub-images. This model is fully verified
when observing measured spectral coherence on open see areas. If scatterers distribution departs from this distribution,
as for manmade structures, spectral coherence is preserved. We investigated the spectral coherence to perform vessel
detection on sea background by using spotlight images acquired on Venice Lagoon. Sea background tends to lead to very
low spectral coherence while this latter is preserved on the targeted vessels, even for very small ones. A first analysis
shows that all vessels observable in intensity images are easily detected in the spectral coherence images which can be
used as a complementary information channel to constrain vessel detection.
The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the
predictions of the OOFELIE Multiphysics software in order to deduce modeling guidelines and improvements. For that
purpose two optical systems have been analyzed. The first one is a spherical lens fixed in an aluminium barrel, which is
the simplest structure found in an opto-mechanical system. In this study, material characteristics are assumed to be well
known: BK7 and aluminium have been retained. Temperature variations between 0 and +60°C from ambient have been
applied to the samples. The second system is a YAG laser bar heated by means of a dedicated oven.
For the two test benches thermo-elastic distortions have been measured using a Fizeau interferometer. This
sensor measures wavefront error in the range of 20 nm to 1 μm without physical contact with the opto-mechanical
system. For the YAG bar, birefringence and polarization measurements have also been performed using a polarimetric
The tests results have been compared to the predictions obtained by OOFELIE Multiphysics which is a simulation
software dedicated to multiphysics coupled problems involving optics, mechanics, thermal physics, electricity,
electromagnetism, acoustics and hydrodynamics. From this comparison modeling guidelines have been issued with the
aim of improving the accuracy of computed thermo-elastic distortions and their impact on the optical performances.
In the past, we developed a holographic interferometry technique based on photorefractive materials for high resolution
measurement of structures deformation. In this paper we present the early results of development of a holographic technique
and facility for deformation and expansion measurement of aerospace composites components. Here the holographic
technique consists in using several illumination beams for retrieving different components of the displacement
vector. In our case the components and structures to be measured in the future will undergo temperatures excursions up
to 150°C typically. Since holographic techniques are sensitive to air turbulences, it is necessary to place the samples in a
vacuum chamber. We will present some early examples of measurements with this facility, obtained for temperatures
excursions ranged between ambient and 29°C as first steps before going further to higher temperatures excursions.
We propose in this paper an integration method of the radar information in multispectral images without disturbing the spectral content. The main problem is to define a fusion rule that allows to take into account the characteristics of these images. Also, the main purpose of this paper lies in defining a new fusion rule performed in the redundant wavelet domain. This rule is based on the Mahalanobis distance applied on the wavelet coefficients. Instead of comparing coefficient-to- coefficient, the distance-to-distance comparison is performed. In this case the selected coefficient in the fused image will be the one that presents the large distance. This approach is applied to fusing the infrared band of SPOT with, respectively, RADARSAT and ERS images. The results show that spectral information is well preserved and there is a better information on the texture and the area roughness.
A quality assessment of InSAR topographic mapping was carried out addressing the issues of feasibility and quality in the particular case of Belgium. We first present a pre-study consisting in the selection of the most appropriate image pairs as well as an assessment of the expected DTM quality, based on interferometric baseline values and ancillary data like cloud cover, humidity, vegetation cover, relief, etc., that influence the coherence level. The quality of the DTM generated from the selected ERS-1/2 Tandem pairs is discussed by comparison with a reference DTM and put in relation with the coherence maps obtained simultaneously with the interferograms.
The frequency domain approach of Scansar problems suffers, numerically speaking, from the constrained smallness of the unit of azimuth increment. This unit is equal to the displacement of the craft between two consecutive transmission times, whatever the burst length, the latter conditioning the resolution of the coherent reconstruction. Thus a large oversampling occurs. There are three main ways of action to save computational effort: (1) The simplest one is to go out of the frequency domain with a dimension reduced transform operating on a cheap manipulation of the full frequential product. (2) The second one is to build the frequential input from several transforms at a dimension close to the burst, thus taking advantage of the initial zero padding. (3) The third one is to modify the 'static' template pipe in order to avoid repetitive operations in the signal pipe. A simple situation will be met where this policy is immediate. A much more intricate case of application leads to a hybrid algorithm connected with the SPECAN approach. The difference between the hybrid algorithm and Specan rests in the strictly diagonal character of the initial transformation performed on the burst in the Specan case, contrary to a narrow band matrix multiplication for the more general hybrid approach. The main lines of conclusion of this study are that, assorted with carefully designed numerical procedures, the frequency domain approach for Scansar is convenient, mainly, for coherent processing of rather longs bursts. More particularly, it combines well with frequential azimuth multilook. In the case of too short bursts, it becomes weaker than direct algebraic manipulation, but it gives an easy way for preparation of the needed static transformation matrices. The comparison with SPECAN approach is less easy, as the nets of points locations for reconstruction do not match. Nevertheless, a static transformation generalizes the Specan concept to prescribed grid by approximations coming from the hybrid algorithm. That new way could be challenging. The important theoretical part of this paper is clarified by illustrative means and some quicklook alternatives discussed in the function of, among other things, the imaging scenario, the required resolution, and the bursts length.