|
<< Click to Display Table of Contents >> Interferometry - Interferometric Tools - Baseline Estimation |
  
|
|
<< Click to Display Table of Contents >> Interferometry - Interferometric Tools - Baseline Estimation |
|
Purpose
This functionality enables to obtain information about the baseline values and other orbital parameters related to the input pair. The extracted parameters have to be intended as approximate measurements aimed at a preliminary data characterisation and interferometric quality assessment. The baseline value itself is not used in any part of the Interferometric processing chain.
A graph, which shows the theoretical relationship between the coherence value and the height measurement standard deviation, pops up at process completion (the graph is not shown if the process is executed in batch mode).
Please note:
The baseline estimation tool give just an estimation of the parameters in the image center, using the flat earth and the approximate theoretical formula. So it cannot be completely representative of the entire image / terrain neither accurate. In any case SARscape will not use this parameter for the further processing. It exploit instead the range-doppler (together with the real terrain height and orbital state vector) for a precise point-wise estimation.
Technical Note
The generation of an interferogram is only possible when the ground reflectivity acquired with at least two antennae overlap. When the perpendicular component of the baseline (Bn) increases beyond a limit known as the critical baseline, no phase information is preserved, coherence is lost, and interferometry is not possible. The critical normal baseline Bn,cr, can be calculated as:
Bn,cr = λ R tan(θ)
2 Rr
where λ is the wavelength, R is the range distance, Rr is the pixel spacing in range, and θ is the incidence angle. Note that the critical baseline can be significantly reduced by the topography.
The sensibility to detect height variations is inversely proportional to the "2π ambiguity height": the bigger the ambiguity height the worse the capability to detect small elevation changes. The 2π ambiguity height AH can be calculated as:
AH = λ R sin(θ)
4π Bn
The sensibility to detect displacements depends on the observation wavelength with the following relationship:
AD = λ
2
In case of Single Look Complex inputs, the output files are multi-looked with the default azimuth and range multi-looking factors.
Input Files
Input Reference file
File name of the Reference data (_pwr for ScanSAR products; _slc or _pwr for all the others). This file is mandatory.
Input Secondary file
File name of the Secondary data (_pwr for ScanSAR products; _slc or _pwr for all the others). This file is mandatory.
Optional Files
Output Baseline Root Name
Name of the output root. In addition to the results for the scene center that will shown up in the pop-up, this file includes the multilooked baseline, height of the ambiguity values and all other parameters for each pixel. This file is optional, if this field is empty, no output file will be created and only the values for the scene center are computed and shown up in the pop-up.
Parameters - Principal parameters
None.
Parameters - Global
It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Other Parameters
It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Output Files
Following information, estimated for the image center, is provided on screen:
| - Normal baseline | Perpendicular baseline (m) between Reference and Secondary orbit. |
| - Critical baseline | Minimum and maximum theoretical baseline (m) suitable for interferometric processing. |
| - Range shift | Shift (pixel), which will be applied in range direction during the Reference-Secondary coarse coregistration. |
| - Azimuth shift | Shift (pixel), which will be applied in azimuth direction during the Reference-Secondary coarse coregistration. |
| - Slant Range Distance | Slant range distance (Reference geometry). |
| - Absolute Time baseline | Temporal baseline between Reference and Secondary. |
| - Doppler centroid difference | Difference (Hz) between Reference and Secondary Doppler centroids. In case the Doppler centroid difference is higher than the Pulse Repetition Frequency (value marked as "critical"), than the SAR pair is not suitable for interferometric processing. |
| - Critical Centroid difference | Minimum and maximum theoretical doppler difference (Hz) suitable for interferometric processing. |
| - (InSAR)2 PI Ambiguity height | Height difference corresponding to an interferometric fringe (2π cycle). The larger this figure the coarser is the capability to detect small height changes. |
| - (DInSAR)2 PI Ambiguity disp. | Displacement corresponding to an interferometric fringe (2π cycle). The larger this figure the coarser is the capability to detect small displacements. |
| - (Stereo Radargrammetry) 1 Pixel Shift Ambiguity height. | Height difference corresponding to 1 pixel shiht. The larger this figure the coarser is the capability to detect small height changes. |
| - (Amplitude Tracking) 1 Pixel Shift Ambiguity displacement. | Displacement corresponding to 1 pixel shift. The larger this figure the coarser is the capability to detect small displacements. |
| - Reference Incidence Angle. | Incidence Angle value (°) of the Reference image |
| - Absolute Incidence Angle Difference. | Absolute Incidence Angle difference (°) between Reference and Secondary images |
| - Suitability for Radargrammetry. | The software provides information, based on the incidence angles of Reference and Secondary, about the suitability of the pair for performing Radargrammetry Processing |
The following outputs are created only if the Output Baseline Root Name is set in the Optional Files Tab.
_dop_diff
Doppler Centroid difference and associated header files (.sml, .hdr).
_N_bas
Normal baseline values and associated header files (.sml, .hdr).
_H_bas
Horizontal component of the normal baseline values and associated header files (.sml, .hdr). It is related to the across-track orbital errors.
_V_bas
Vertical component of the normal baseline values and associated header files (.sml, .hdr). It is related to the radial component of the state vectors.
_Reference_sr_dist_
Slant range distance (Reference geometry) and associated header files (.sml, .hdr).
_2PI_amb
Estimated ambiguity height corresponding to a phase cycle and associated header files (.sml, .hdr).
_az_shift
Estimated shift in azimuth direction and associated header files (.sml, .hdr).
_rg_shift
Estimated shift in range direction and associated header files (.sml, .hdr).
_shift_amb
Estimated ambiguity height corresponding to 1 pixel shift (for flat earth approximation) and associated header files (.sml, .hdr).
_Reference_lia
Local Incidence Angle of the Reference image
_Secondary_lia
Local Incidence Angle of the Secondary image
Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.
General Functions
Exec
The processing step is executed.
Store Batch
The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.
Close
The window will be closed.
Help
Specific help document section.
Specific Function(s)
None.
References
F. Holecz, P. Pasquali, J. Moreira, E. Meier, D. Nüesch: "Automatic Generation and Quality Assessment of Digital Surface Models generated from AeS-1 InSAR data". Proceedings of European Conference on Synthetic Aperture Radar, Friedrichshafen, Gemany, May 1998.
D. Small, P. Pasquali, S. Fuglistaler: "A Comparison of Phase to Height Conversion Methods for SAR Interferometry".
Wolfgang Goblirsch, P. Pasquali: "Algorithms for Calculation of Digital Surface Models from the Unwrapped Interferometric Phase". Proceedings of International Geoscience and Remote Sensing Symposium (IGARSS'96). Lincoln, Nebraskq USA. May 27-31.1996.