Topic: General Information


Firstly, i would like to point out that i am a new user of the CosiCorr. I am trying to determine the mass movements by cosicorr. However, i have got some questions. I would be too pleased if you could answer them.

I have got two ASTER (L1A *.hdf) images in two different periods. I want to determine the mass movements(about 5-10 meters) between two periods related to study area.

First of all, i wonder the answer of these questions.

I think we should use GCPS (5-6 GCPs in two images by Image to Image) in stead of orthorectification by ancillary file (about accuracy of 100 meters). We need also to a good DEM. Generally, you should suggest the shaded DEM for orthorectifying. We can have some difficulties to determine location of the tie points in shaded DEM.  On the other hand, in case of having the high resolution data (quickbird image, orthophoto or toposheet), can we use them for converting from tie points to GCPs? If we use them, Do we encounter any problems? During the orthorectification, if needed, which one of the optimized GCPS or GCPS should we use with DEM?

In correlation file or nlmfiltered file,  Data represents what (in Cursor/Location Value window),and what is its unit (metre or pixel)? For example, what does it mean in case of data:-12.125171.

Processes performing for my study

1. I applied the orthorectifications (by using ASTER GDEM) for images in two periods without GCPS.
2. I have the correlation file and it appears good.
3. I applied the filter the SNR Band of the correlation file (between 0.9 and 1)Discard / Replace images values
4. I defined subset area in the region without NaN values and determined  the h parametre for nlmfilter.
4. Although i applied nlmfilter for EW and NS bands, i have still some NaN values. How can we get rid of these NaN values?
5. Should i apply the destripe image for nlmfiltered image? if it should be, which one of files should we select for Automatic Orientation (in image destriping / undulation removal)

Thank you in advance.


Re: General Information


Sorry for my late answer. I actually answered to that message a week or two ago, but looks like my message was lost. Anyway:

- There are two kinds of "GCPs". The first set of GCP is used to constrain the first image, which will become the Master image. This first set of GCP exists to make sure that the absolute georeferencing of your images is correct. In particular, the registration of your master image with respect to the DEM used during orthorectification should be good to avoid topography artifacts. It's the reason we usually recommend selecting the GCPs of the first image wrt the shaded DEM. It is true that if the shaded DEM is featureless, then this technique won't work. Can you use another image to collect the GCP of the first image? Yes, of course, but you have to make sure that the other source you might be using (Quickbird, etc), is well registered to the topography model used for orthorectification. It's all a matter of consistency: make sure your process flow is consistent.

- The second set of GCPs should ensure that the ortho-images you're producing are very well co-registered. For this step, you should not use another source of data. For this step, you should select the GCPs of the second image with respect to the first ortho-image. This second set of GCPs ensures accurate relative georeferencing.

- The NaN values indicate missing values and you should not try to get rid of them. The NLM filter tries to reduce the noise, it doesn't invent data when it's missing. Anyway, I don't think you'll be very successful in using the NLM filter with ASTER images as noise level is usually quite high.

- Destriping is often necessary with ASTER images.

Hope this helps,