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Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Tue Feb 26, 2019 9:43 pm
by samuellow
Hi all at PODAAC!

Thank you for putting together such a wonderful repository and community of information and people. I am interested to retrieve actual ranging measurements between GRACE A and B (no particular epoch in mind). My research purpose is to use actual ranging measurements as validation to a GNSS-based inter-satellite distance measurement algorithm I am working on for satellites (i.e. moving baseline measurements).

I have downloaded some data from the FTP, I believe the range data is prefixed at KBR (K-Band Ranging?). However, the file is encoded in binary; I spent quite a bit of time trying to compile the binary-to-ASCII code so I could make it readable. Didn't seem to work of course, and so I eventually gave up and would like to ask if anyone knows where to retrieve ranging measurements of the two GRACE satellites :)

Is there a guide for this?
Cheers
Sam

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Tue Feb 26, 2019 10:11 pm
by samuellow
So I actually already found the range measurements file (or at least I think this is the right one, please tell me if it is wrong!)

https://drive.google.com/open?id=1ukajiEFqxiFgAYS57G6G0SlbntaH_e8N

https://drive.google.com/open?id=1m_LTLBQqUEUlS7GDawQ2d9RUr2ZR8_Fn

I am specifically looking for the distance between the two satellites on 2010-07-27 (24 hour data set if possible).

Could anyone help me with the conversion? I can't seem to get the C compiler to work on Windows 10... Also, even after conversion, how may I interpret the file? Where would one find the column that gives the desired inter-satellite range values?

Thank you all :)
Cheers
Sam

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Wed Feb 27, 2019 12:03 pm
by wenhaoli
Hi Sam,

Unfortunately, you have to compile the binary-to-ASCII code in order to access the GRACE Level-1B datasets, which are in binary format. The next release (RL04), which may come out by the end of year, will be in plain ASCII format.

I know it is hard to compile the binary-to ASCII code which was developed ten years ago. Could you tell me what the problems are when you compile this code? Let's try if we can make it work on your machine.

Best Regards,

Wenhao Li
PO.DAAC data engineer

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Wed Feb 27, 2019 4:33 pm
by samuellow
Hi Wenhao. Thank you for the quick reply! I am using gcc on Cygwin (windows) but from the README I think the compiler seems to only run on Linux based OS's. Thus it fails to compile, throwing errors. I will attach a screenshot of the error later. I have not tried other compilers like MinGW on Windows yet.

Alternatively, if I may ask for anyone's kind gesture to help with the compilation and running the exe file to convert from Binary to ASCII, that would be great! My email is sammmlow@gmail.com :D

I saw some sample ASCII format data for KBR but I am not sure how to read it. Is it listed as XYZ range and am I supposed to take the root mean square of the XYZ components to get the true KBR range? Thank you!
Cheers
Sam

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Mon Mar 04, 2019 12:21 pm
by wenhaoli
Hi Sam,

Sorry for the delay. Yes, you are right that the software is only run on Linux based OS's.

Regarding to your question about using the KBR file, you can find the detail information from GRACE Level-1B handbook (ftp://podaac.jpl.nasa.gov/allData/grace ... B_v1.3.pdf). For more related GRACE info, you can visit the PO.DAAC GRACE mission page at: https://podaac.jpl.nasa.gov/GRACE.

Best Regards,

Wenhao Li

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Tue Mar 12, 2019 6:14 am
by samuellow
Thanks Wenhao! I'll try it on a Linux distro and hopefully it works. :)

Re: Extracting GRACE Inter-Satellite Range Measurements

PostPosted: Wed Mar 13, 2019 7:11 am
by samuellow
Hi Wenhao! I have tried compiling and making using gcc on Cygwin64 on Windows, and using gnu_make on Linux Ubuntu 16.04... Both have failed terribly and have spent days trying to get the software to actually compile and make, it has been quite exhausting really. I have the error logs from Ubuntu attached here:

https://drive.google.com/open?id=1NQIeA ... w4OyDrJ14a

ErrorLog1 was the first time trying to run gnu_make on it, and ErrorLog2 was the second time running it after the first failed attempt. "Directory" basically shows the printed working directory of where I was.

Alternatively, could I request for anyone's help to transform KBR data for 2010-07-27 into ASCII format using the binary-to-ASCII converter that is used for GRACE? It is a one-off request and I wouldn't want to trouble anyone here otherwise, had it been so urgent for me to retrieve this data. If someone would be so kind to, I have attached the KBR files here.

https://drive.google.com/open?id=1ukaji ... lbntaH_e8N

https://drive.google.com/open?id=1m_LTL ... RUr2ZR8_Fn

I am also wondering, how do you interpret the data in the ASCII-format KBR files? The Level 1B Manual does not explain this very clearly (no indication of what the headers of columns mean etc). I have seen one sample one that comes with the release of GRACE Level 1B data but it is for a different date. How do you interpret the rows and columns of numbers to extract the true range measurements? A snapshot of the default 5-min length ASCII file for KBR (2003-09-14) is shown in the link below.

https://drive.google.com/open?id=1mEFXl ... tvuI9Kn2pj

Thank you very much
Cheers
Samuel Low