- Introduction: basic proposed geometry & motivation for this bistatic activity - Description of the SBX receiver - Some aspects of bistatic processing and Interferometry - First results of imaging and single pass interferogram on the Barcelona harbor - Conclusions
Using a SAR satellite as a transmitter of opportunity, bistatic SAR raw data and images are obtained from the echoes recorded by ground receivers The motivations: - Research on wide angle bistatic scattering and image interpretation which is expected to differ from the monostatic or quasi-monostatic cases Source of experimental SAR raw data in flexible RX configurations: SAR processing, multichannel SAR: interferometry, polarimetry, tomography, etc. Example: shown in the image 3 receivers operation in Differential Interferometric model would provide the 3D subsidence vector information Affordable education covering the whole SAR chain: SAR systems/processing/research/new applications wide an The Sabrina’s possible applications are the following. The first one and which will be presented here is a DEM generation using across track single interferometry. This application is the first one to be done if future complex differentials applications are wanted to be carried out. Another one, in which we have done some studies and we are working on are MTI applications using along track single pass interferometry. Also differential applications can be performed using sabrina, such as terrain deformation monitoring. That can be interesting due that more than one receiver can be used in each acquisition and they can be placed in different locations allowing the extraction of the 3D terrain deformation component. Well, also all the fact that more than one receiver can be used in each acquisition can allow the use of multibaseline techniques in a single pass mode, avoiding the temporal decorrelation.
Ok, lets define the bistatic resolution and compare it to the monostatic one For the monostatic case, the range resolution, depends inversely to the sinus of the transmitter incidence angle with respect to the normal of the terrain. However for the bistatic case, it depends inversely to the sinus of the transmitter and receiver incidence angles with respect to the normal. About, azimuth, the bistatic resolution is slightly worse than the monostatic, it losses a factor due to the one way path and gains a factor sqrt of 2 due to the 1 way transmitter diagram antenna. The result is a loss of resolution of a factor sqrt 2
Lets pass to describe the acquisition scheme for single pass interferometric data using a fixed receiver. ERS or ENVI are used as a transmitters of opportunity and two antennas are placed on the ground, with a certain baseline, illuminate the area of interest. It is important to notice that due that receiver is near to the scene, the incidence angle, range to the antenas and baseline are variying along the scene. We can distinguish between two acquisition configurations, backward scattering and forward scattering. In fact, both of them are forward scatt due that the path from the transmitter to the scene and the path from the scene to the transmitter are different in both cases. Well, then we call back scatt when the transmitter and receivers are on the same side of the area of interest and forward when they arent As in the monostatic case, the information resides in the difference of the intereferometric phase between nearby points. Well this formula is similar to the monostatic one, with the difference of the factor 2, due to only one way and taking into account that baselins, range and incidence angle vary along the illuminated area.
BISTATIC SAR BASED ON TERRASAR-X AND GROUND BASED RECEIVERS A.Broquetas, M.Fortes, M.A.Siddique, S.Duque, J.C.Merlano, P.López-Dekker, J.J.Mallorquí, A.Aguasca Remote Sensing Laboratory (RSLab) Universitat Politècnica de Catalunya, Barcelona
Illumination envelope, coarse PRF and pulse replica are obtained from direct illumination channel
From range compressed pulses accurate time alignment of both direct and scattered signals is achieved
The frequency offset between TSX and SABRINA is estimated from the pulse to pulse phase change
Azimuth focusing is based on Backprojection
Direct + scattered Spectrogram
Range compression with Chirp replica and receiver equalization Direct pulse compression evaluation Green: compression with linear FM chirp Blue : compression with chirp replica & RX H(f) equalization Received spectrum Receiver H(f) Equalized Receiver H’(f)
Bistatic SAR with fixed ground receivers allows to develop affordable complete SAR chains suitable for hands-on SAR training and multichannel SAR research
A multichannel X-Band SAR receiver has been designed by undergraduate students from low cost COTS monolithic devices
First results on Barcelona harbor using TSX illumination has shown the importance of acquiring clean direct channel replica and channels H(f) calibration/ equalization for accurate range compression and InSAR
Metallic containers and ships produce very bright scattering centers even at wide bistatic angles
The cost of high speed digitizers is presently the main bottle-neck for budget multichannel operation. A PRF trigger is under development for longer acquisition at highest sampling rate