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Dear users,
We think that some updates with respect to the previous post can be useful since more than 5 years have passed.Q: What are the orbits used for Sentinel?
A: You can find useful information in the section 2.5 of this document at the following link:
https://sentinel.esa.int/documents/247904/3372484/Sentinels-POD-Product-Handbook.pdfQ: Where can I download the orbit files?
A: SARPROZ will automatically download the correct orbit files (the most precise available at the date of the session). If your computer has internet limitations and you need to download the orbit files manually you can download them here: https://scihub.copernicus.eu/gnss/#/home
Username/Password are the same for every user and they are: gnssguest/gnssguestQ: How do I know what orbit files are used for each image data?
A: SARPROZ is always communicative and generous with information 😉
In the terminal (if you are using the compiled version) or Matlab command window (if you are using the pcodes) you will find all the information about the orbits used for each image after setting the orbits in the SLC data import module.Good morning Yunus,
from my experience, at the moment I do the same, i.e. using the multi-sense module or external GIS-based tools to produce the maps of Vertical/EW motion with some spatial averaging.About the time series, what I do is to apply use the same formula used to derive the maps applied to some specific points, manually.
The possibility to create synthetic time series from ASC and DESC data is affected by the fact that the original data are usually acquired at different dates.
In some cases for some areas in the world you may find Sentinel-1 data acquired on the same date for ASC and DESC and this makes the thing more accurate.Best,
AlfredoHi Bridgetwang.
If you create 3 different projects, it means that you are going to use 3 different Master images for the Coregistration step. For this reason, the final matrix of the coregistered images, such as all the parameters like the reflectivity map and other data will be very similiar but not identical. This is also true for the azimuth/range coordinates of targets. The same object (e.g. a building) will be located in different positions for the 3 different projects.
For this reason, you cannot use the same RefPoint.mat file for all the projects.However, since the area is the same, I am pretty sure that you can easily find the same target to be used as a reference point in the Reflectivity Map of each project. Take note of the line/sample coordinates and then select the point in the proper section of the APS panel by selecting the “Manual option”.
regardsHi Mehrnoosh,
usually, the best approach is to keep a quite large set of range taking into account the expected values by considering:
– the characteristics of your AOI (e.g. presence of high rise buildings);
– the type of graph you created (long connections, short connections, etc. )Once you have a preliminary estimation, you can have a look at the histograms (as you correctly did) in order to be sure that the distribution is fine. To be more clear, in the -5+5 estimation you have too many connections estimated in the extreme bins and this is not good since it means that higher and lower values exists and they are probably not properly estimated.
Still the same condition is present for the -10+10 (see the peaks at the limit values). The 25 an 30 values are much more better. Keep much larger ranges will not lead you to a better result.
regardsDear all,
the policy of ESA for the distribution of orbit data is changing over the last months.The automatic download will be implemented again in SARPROZ soon.
In the meanwhile, you can go on by downloading the orbit files manually. Once downloaded, you can load the orbits in SARPROZ by using the procedure described at the following instructions: https://sarproz.com/manual/slc_data_module.html
To manually download the orbit files, you have to register an account at the ESA Earth Online portal https://earth.esa.int/web/guest/home
Click on “Register” (top of the page) and create an “EO-SSO” account. Then, once logged-in in the “MyEarthnet” section:
1) click on “Data Access–> Browse Data Products” then search for “DORIS Orbit” and click on “Get Data.
2) The system will ask you to provide some information (geographical extent of your area of interest, application field, a short summary of your activities. If you want, you can say that you are going to use such data with SARPROZ);
3) Once the request is accepted (usually, near-real time), you will find the product in the “My Online data” clicking on the “MyEarthnet” section (top of the page).
4) for the PRARE Precise ERS orbit (PRC) do the same procedure from the point 1 (you will probably not asked to fill the module described at point 2 again).
cheers
Hi Cecilia, in order to better understand the issue, could you please attach a picture of the Asc and Desc results (PS) you imported in the decomposition module?
Hi Yasser,
the APS module, is the “core” of the multi-image InSAR process (say PS, QPS analyses). As you probably know, to extract as more information as possible from your dataset, all images need to have the same technical features (resolution, incidence angle, polarization, etc.).
Also the number of images is very important. If you have only few images it will be quite impossible to achieve good results (20-25 images is the minimum for reliable results).
I will send you an e-mail to pass you my contacts for further assistance.Regards,
Alfredo
Hi Anarizka,
1) Here my personal suggestion about your first question. The best way to understand the goodness of your results (both preliminary and final) is based on the knowledge about the process you are investigating. You should address your specific case study (landslide? subsidence? localised structural issues?) being driven by a general model based on geological/geophysical or structural information. In such way you will be able to judge your results by means of a robust model.
About your specific question, please consider that the multi-image InSAR is a basically a challenge against atmosphere and other noisy signal (e.g. orbital inaccuracies). For such reason, you will reach your target when you are able to separate the “real” signal (i.e. height, displacement information, seasonal deformation, etc.) from the noise given by atmosphere phase effect and others. To do this, all steps are fundamental. In the APS panel you have several steps to be considered: a good selection of PS candidates (set of points); a robust network (the spatial graph), and the estimation of preliminary parameters along connections of points (usually height and displacement as linear trend – but also, sometimes, non linear displacement). Once you get your parameters, you need to spatially invert the graph to get parameters on individual points. At this stage, if the temporal coherence is high on most of connection, the estimation of APS by using IR will be good (high coherence) for the whole set of point by using IR, which is a standard for all PS-like approach (you will find lot of reference about this). If it is not, you should investigate if other source of noise exists with a spatial distribution (few points? points too sparse? orbital inaccuracies?). As Prof. Perissin said, in fact: “…in some more complex cases, the final coherence may be not satisfactory. Such cases should be analyzed one by one to understand the reason of the failure.”
In such cases, if you judge your preliminary results good (remember the “conceptual model” I mentioned in the first part of my answer) and if you trust them, you can try to use IP instead of IR, thus forcing the solution because “you” decide that it is correct. Unfortunately, there is not “one perfect way”. InSAR is based on data (you have to analyze them carefully) there is not a standard way to perform all analyses: every case is a singularity and only by experiencing several case studies you will be able to find the correct way.2) It depends on what you want to do. It is not a matter of heights (lowlands and so on). If you ignore Ext.DEM and you use the spatial filter, you are simply not performing a standard “PS” analysis, and you are switching to distributed scatterers analysis (Quasi-PS, etc.) (please refer to http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5978217). Such analysis is based on a totally different approach and also other aspects should be taken into account (e.g. the image graph which should maximize the spatial coherence, as the MST, for example).
3) Coher exploits the spatial coherence written in previous steps to weight to parameter estimation, while amps use the reflectivity value (it stays for amplitudes). If you choose none, any weights will be used. Indirectly the APS can be influenced by this step since it influences the parameter estimation (which is the starting point to estimate the APSs).
best regards
Alfredo