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yacob

NEXRAD Precip Problems

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Hi,

I am attempting to use observed precipitation data that I have aquired from TRMM (Tropical Rainfall Measuring Mission) in my GSSHA project. The data is spatially and temporally varied and I have converted it to the arcinfo grid .asc format. I am using the WMS Nexrad Radar grid conversion tool to preprocess my precipitation into the .gag file. The data is near real time, 3 hourly global precip at 0.25 degrees (-180 to 180 lon and -60 to 60 lat). When read in a 48 hour rainfall (which composes of 16 asc files) I get weird values in my .gag file. It appears that values for a given gridded gage seem to double which does NOT match the .asc file...at all. I get output like this in my .gag file

0.0

0.0

0.749

0.0

0.749

0.0

0.0

1.499

2.997

0.0

0.749

5.994

12.738

0.0

0.0

26.045

As you can see it starts to get exponentially out of control. I have tried doing Judy's Branch Tutorial (using NEXRAD raw data) and found that the .gag file looks normal after adding radar data. The only difference between the TRMM and the NEXRAD is that TRMM is global and I am building a model that is located outside the US. Can WMS help me build a precip file using the NEXRAD radar option with data that is not NEXRAD but is still in the correct arcinfo grid format or do I have to build the .gag file myself? Thanks.

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Hi Yacob,

Thanks for your email. You should be able to use any type of Arc/Info ASCII grid file to compute the data for your GSSHA rain gage file. The best thing for you, if you have followed the steps in the documentation and they do not work, is to do is to contact Aquaveo Tech Support using one of the methods described on this page: Aquaveo Tech Support. You will probably need to send them the files you're having troubles with and probably your GSSHA model so they can figure out the problem.

Thanks,

Chris

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Hi Yacob,

Thanks for your email. You should be able to use any type of Arc/Info ASCII grid file to compute the data for your GSSHA rain gage file. The best thing for you, if you have followed the steps in the documentation and they do not work, is to do is to contact Aquaveo Tech Support using one of the methods described on this page: Aquaveo Tech Support. You will probably need to send them the files you're having troubles with and probably your GSSHA model so they can figure out the problem.

Thanks,

Chris

Hi Chris,

Thanks for your help. I figured out how the precip data is spatially recorded in the GSSHA .gag file and wrote a program to print RADAR data for all precipitation events. The way wms reads spatial precip is as follows

Suppose arcinfo ascii file below with indicies 1 to 20. WMS reads the precip file from 1 to 20, and loads only those values in the file that fall within your watershed. (The best way to visualize this is to load the ascii file and a polygon of your watershed into ArcGIS) WMS then stores them in the .gag file as RADAR YYYY MM DD HH MN 1 2 3 ... 20. i.e. if your watershed polygon only covers 9,14,3,8,13,18,7,12 then your RADAR line will read RADAR YYYY MM DD HH MN 3 7 8 9 12 13 14 18

5 10 15 20

4 9 14 19

3 8 13 18

2 7 12 17

1 6 11 16

If WMS is giving you a hard time with this, just recreate the same process with your own code. As long as it is in the right format, GSSHA will read it. Also, if you import a nexrad .asc file and save the project, it will write out your coordinates in the .gag file. So keep this part of the file and paste your precip data underneath.

This is just the way I did it; it may not be applicable to everyone.

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