Motion measurement errors analysis for the “one-active” LASAR
The influences of the motion measurement errors (MMEs) to the 3D SAR imaging are analyzed based on the “one-active” LASAR system in this paper. Firstly, the principle and the spatial ambiguity function (AF) of the “one-active” LASAR are introduced. Then the 3D MMEs are introduced according to three forms: the 3D velocity errors and the 3D acceleration errors, the sine vibration errors and the array vibration errors. The 3D SAR system's maximum allowable MMEs are obtained and the influences of the 3D MMEs to the 3D AF are analyzed by the numerical simulation. Finally, the ground experiments and its results are presented, which validate the feasibility of the “one-active” LASAR.
POLINSAR for FOPEN using flashlight mode images along circular trajectories
The airborne radar system RAMSES collected data over the Sweden forest to investigate the capabilities of detection at P-band and influences of different SAR parameters like resolution, central frequencies, and look angle. During this campaign, circular trajectories have been performed in order to analyze the presence of anisotropic scattering from the targets at P-band. We show the treatment of two circular trajectories using the Flashlight imaging mode and its ability to collect several SAR data with different look angles. The scope of this paper includes a general description of the operating mode of flashlight SAR images in the interferometric mode and the use of it for FOPEN purpose. The capabilities of detection of such polarimetric images have already been investigated, but without using the interferometric mode [1]. It had been shown that using circular trajectories at P-band was necessary to detect targets: first in our configuration detection was very difficult because the forest was very dense, secondly the targets were very sensitive to the orientation angle of the radar, which should not be the case at lower frequencies. Moreover, polarimetry and polarimetric interferometry are useful tools once the acquisition conditions ensure that detection is possible. Now, the full polarimetric and interferometric information are used in order to explore the potential of the POLINSAR circular mode to yield high detection rate.
FOPEN with Polarimetric Interferometry: Validations with Experimental Data at P-Band
ABSTRACTAmong the POLINSAR data beneﬂts, we can ﬂnd the possibility of extracting several forest parameters. Usingthis forest parameters estimation, it is possible to enhance the detection of targets hidden beneath foliage. Thesecapabilities have been already demonstrated by Cloude using L-band SAR simulations [3, 4]. The key idea is tomodel the forest by a random volume whose interferometric coherence is invariant to changes with polarization.A new method is suggested which is based on a modelling of the forest more adapted to the P-band. Thepotentials of these methods are tested with real SAR data provided by the ONERA airborne system RAMSES.Full polar P-band data acquisitions during January 2004 over the Nezer pine forest (France) are used forinterferometry in a repeat-pass mode. The site, managed for several years by INRA (the French NationalInstitute of Research in Agronomy) contains many crops of maritime pines of diﬁerent ages and diﬁerent heights.The oldest crop contains 52 years old trees; two targets are hidden inside this stand: the ﬂrst one is a metallictrihedron, the second one is a truck. Important improvements in the detection of both targets are demonstrated.However, the principal di–culty lies in the rather signiﬂcant number of "false alarm" whatever the method maybe considered. Finally, the paper proposes some guidelines for reducing the "false alarm" number using atime-frequency analysis.1 INTRODUCTION1-1 The RVoG limitations in P-bandIn recent years, some experimental and theoretical studies have been carried out to demonstrate the poten-tial of PolInSAR in retrieving forest parameters. Also a theoretical model have been developed to establishrelationships between the interferometric coherence and the physical parameters of vegetation: total height,extinction and ground over volume ratio. This model describes the forest using a randomly oriented volumeover a ground. It has been developed by B.Treuhaft [1], studied and generalized by Cloude and Papathanassiou[2]. It is called the RVoG (Random Volume over Ground) model. Although this model is commonly used withdata at L-band and C-band, and provides a good understanding of the problem, it is not accurate enough forP-band: the nonuniform orientation distribution of trunks signiﬂcantly aﬁects the results on the vegetationscattering phase centers. Moreover it has been demonstrated previously that double-bounce strongly in°uencesthe total response, but it is not taken into account in the RVoG model. P-band data require a model involvingthis mechanism.1-2 The "COSMO" model"COSMO" [5, 6] models the vegetation as a set of discrete cylinders representing tree components. Electric ﬂeldsscattered by each element are added coherently and attenuation is computed by means of Foldy’s approximation.COSMO is able to provide information on the respective in°uences of the diﬁerent mechanisms. It is thenvery useful to understand the backscattering mechanisms of a forest. Using this model, accurate statistics ofthe scattering phase center heights are calculated numerically [7]. The validity and accuracy of COSMO aredemonstrated by comparing the measured interferometric phases to the scattering phase center heights of severaltest stands in a SAR image. However, this model is much more costly and its inversion is very di–cult becauseof the numbers of parameters. An alternative solution is to use "COSMO" in order to determine what are theimportant descriptive parameters, and to deduce a simpliﬂed model, which will be called "TRV model".