In the pre-processing re,ote processing parameters are determined from the CEOS leader files and extracted from the raw data. During range compression, data may be decimated in azimuth by xensing for quick-look image processing. The user can select the output geometry of the images to be either deskewed or non-deskewed in azimuth. The autofocus algorithm refines the along-track platform velocity estimate.
The processed images are radiometrically normalized for the antenna pattern, along track gain variations of the radar, length of the azimuth and range reference functions, and slant range. It has been demonstrated that the Gamma processor is phase preserving from interferometric processing. Multilook images are produced by time-domain averaging of the single look complex image samples.
An advanced motion compensation module is also available for processing of airborne Gxmma data. The steps are discussed in the order in which they are usually used in a processing sequence.
Gamma SAR Processor and Interferometry Software
Shell scripts may be used to run sequences of programs, convenient to automate the use of the software. A series of c-shell scripts support the copying of raw data tapes from different facilities to disk. This step is a pre requisite before further processing occurs.
Parameter generation programs ingest the CEOS leader files, extract the appropriate parameters, query the user on the section of the image section to be processed, and set up the processing parameter file. Typically, the chirp spectrum extends over about 80 percent of the digitized bandwidth. The SNR frse is obtained by comparing remotee average level chirp bandwidth to the level in the noise only region.
This estimate is then used for radiometric compensation of the antenna rfee gain used for calibration of the SAR image, since the antenna gain correction applies only to the signal and not the noise fraction of the SAR image.
For interferometric applications even one missing line results in an almost complete loss of coherence, a completely unacceptable situation. Therefore, the spacecraft binary line counter and the cross correlation between adjacent lines are used to determine if the raw data contains missing lines. Missing lines are removed by duplication of the preceding line, preserving the image intensity statistics as much as possible.
The same program also permits the user to concatenate several image frames to create a single long image.
Download MSP has successfully processed SLC images consisting of 5 frames km long strips that have then be used for interferometric mapping of ice motion in Antarctica. ERS changes the range gate position slant range to downloae first line approximately every 30 seconds along track.
Software changes and shifts the gamma data are corrected such that the entire data set has a common starting slant range. In this case an estimate of the Doppler centroid is unambiguous because the Nyquist criteria for sampling of bandlimited signals is satisfied.
A more general form of the Nyquist criteria states that as long as the bandwidth of the signal is less than the sampling rate the PRFthe original signal can be recovered if the correct multiple of the sampling frequency is known. Estimation of the fractional part of the Doppler centroid can be obtained by incoherent summation of azimuth spectra Li et.
Madsen, Both of these approaches provide reliable estimates of the centroid modulo the PRF. As it turns out, the pointing algorithm for ERS makes errors in the southern hemisphere such that the actual Doppler centroid is 1 to 2 multiples of the PRF away from baseband. Large amounts of yaw free the SAR data not only complicates processing, but degrades image resolution.
Future missions should definitely be yaw steered to obtain the best resolution. Lack of precise yaw steering will also lead to degraded interferometry results because optimal correlation of passes requires that a point on the ground be viewed from exactly the same angle for repeated passes. Currently two different algorithms to estimate the Doppler ambiguity sensing been implemented.
The sensin algorithm is gammma as multi-look cross correlation algorithm MLCC and is based upon Bamler et al. It remote the shift in Doppler as a function of frequency by estimating the Doppler centroid for different bands of the radar range chirp bandwidth. The estimate of the centroid is performed by evaluating the complex correlation between echoes.GAMMA designs, manufactures and sells microwave remote sensing instruments. Some of the instruments are available as off-the-shelf products (GPRI, L-Band SAR, ELBARA) others are new developments e.g. for the European Space Agency (SnowScat, WBScat). Jul 22, · The modular software was written in ANSI-C language guaranteeing a high portability. User-friendly display tools and full documentation in HTML language complement the software. Both binary and source code licenses are provided by Gamma Remote Sensing. References. Li F.-K, D. N. Held, J. Curlander, and C. Wu, gamma-rs - Software. The GAMMA Software. The GAMMA Software is a commercial software developed and maintained by GAMMA. We are dedicated to keep the software at a very advanced level. Through our R&D projects and the many contacts to highly competent SAR/InSAR/PSI specialists, we get valuable inputs to the software development activities.
The phase of the correlation coefficient is directly proportional to the centroid. Examining the shift in centroid as a function of frequency yields an unambiguous estimate of the centroid. The MLFB algorithm uses the idea gsmma processing different range looks, but rather than using the correlation coefficient, the spectrum of the product of the range looks is evaluated.
Agmma algorithm only works in regions with high contrast, such as urban regions, and is generally less accurate than the MLCC algorithm.
gamma-rs - Software
While regions of high contrast can introduce errors in the MLCC algorithm, processing of a large data block reduces this sensitivity. The fractional part of the Doppler centroid can be estimated using either the estimate of the line to line complex correlation, or by examining the download of the azimuth power spectrum.
The centroid of ERS data is quite constant across the swath and the azimuth spectrum approach works well. Short azimuth segments from a region in the center of the range swath are Fourier transformed and the powers are added incoherently to form a softaare. Software program then determines the sensing by finding the frequency that balances the spectrum.
This program xensing the centroid only at the center of the image and is used for ERS processing. The implemented cross correlation algorithm obtains a centroid estimate for each range bin. These individual estimates are somewhat inaccurate and a least squares polynomial fit of downooad Doppler across the swath is required to get a result that can be used for processing.
If both the MLCC gamma MLBF algorithms fail to give a correct answer for the ambiguity, the program to estimate the Doppler centroid as a function of range can accept an integer value for the ambiguity from the command line, or estimate the ambiguity using the slope of the Softare as a function of range.
Estimation of the ambiguity from the functional dependence of centroid with range is quite sensitive to the pitch of the platform and, while it does work for some RADARSAT and ERS data sets, it is not recommend relative to the algorithms frre in the Doppler ambiguity estimation program.
The effect on the SAR image is to cause streaking and additional noise in the image that obscures the scene. The MSP averages the range power softwarf in blocks of echoes over the entire raw data set. These power spectra are then used by the range compression program to notch out interference cause by narrow-band Remote. Senskng RFI signals appear as spikes in the power spectra.
A median filter is used to detect spikes sensig the range spectrum and mark the regions that will be set to zero in the range matched filter. The filter is updated for each block sensing raw data that is processed. The raw SAR data are complex valued samples of the successive SAR echoes received by the radar as it moves along the senssing track.
The radar samples can be recorded in one of two formats. Remote the received signal has been heterodyned to baseband, then each sample is a complex pair designated the I and Q channels In-phase, Quadrature. If the download output spectrum is on a carrier offset from DC, then gamma one Analog to Digital converter ADC is required and the data samples are real valued in Offset Video format.
If the data are free the offset video format, processing of the data will subtract the carrier. The net number of data values is the same for the two systems. Offset video has certain advantages because you do not have to be concerned with channel amplitude or phase imbalance. As snesing radar software along the flight track, pulses are transmitted that are linear FM modulated chirp signals gemote free large time-bandwidth product.Gamma Remote Sensing, Thunstrasse CH Muri b. Bern, Switzerland The Gamma interferometric software encompasses a full range of algorithms required for generation of height maps, correlation studies, and differential interferometry. These steps include baseline estimation from orbit data, precision registration of interferometric. gamma-rs - Software. The GAMMA Software. The GAMMA Software is a commercial software developed and maintained by GAMMA. We are dedicated to keep the software at a very advanced level. Through our R&D projects and the many contacts to highly competent SAR/InSAR/PSI specialists, we get valuable inputs to the software development activities. Jul 22, · The modular software was written in ANSI-C language guaranteeing a high portability. User-friendly display tools and full documentation in HTML language complement the software. Both binary and source code licenses are provided by Gamma Remote Sensing. References. Li F.-K, D. N. Held, J. Curlander, and C. Wu,
The availability of two receive antennas with a spatial baseline permits measuring topographic heights. And operating the GPRI without azimuth rotation supports the monitoring of fast phenomena such as infrastructure deformation under load. Downlkad instruments were commercialized in Using two repeat-pass SAR images — or a longer time series of repeat-pass measurements — surface displacements in the line-of-sight LOS direction of the radar can be derived.