Wednesday, August 1, 2012

How to get ASCAT Winds from Saildocs

We have several articles in this series about ASCAT. Search the blog on ASCAT to find them.  We at one point (2012-2014) had an email service of our own that provided these by email request, but we discontinued that primarily due to hacker attacks... maybe we will look into this later, but then we added this note:

For completeness, we should mention there is another way that you can customize to this task using the very nice email service of saildocs, which is well known to many cruising sailors, though I would guess not many are taking advantage of this powerful feature of the resource.

First we will need some preparation to know what files we need for the regions of interest. These are obtained from the graphic index at http://manati.star.nesdis.noaa.gov/datasets/ASCATData.php.  Go to that map and put your cursor over the region of interest and note the file name in your status bar. There are two index maps, one for ascending passes, the other for descending passes. You will see the file names are very similar.

The world is divided into small Lat x Lon segments of 10º x 15º in size.

Then the process is very simple:

Send an email like this:
----------------------------
 TO:  query@saildocs.com
SUBJECT:  anything

BODY:
Send http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBds86.png
---------------------------
Then in a few minute you will get the graphic image of the winds you want. This will always be the latest data, but the latest may be some hours old depending on latitude and time you ask for it. The trick is to make your own index of the regions you care about and you can ask for several in a row to get what you want.

That is, you would immediately ask for the ascending pass with:

Send http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBas86.png

The 86 is identifies the region 30N-40N x 75W-60W,  and the as vs ds identifies the pass, Ascending or Descending.

The file size for this 25-km resolution will be about 35 kb. The larger overview at 50-km will be about twice as big.

The above sample is for waters around Bermuda.  If you want HI waters use

HI North
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBas15.png
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBds15.png

HI South
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBas16.png
http://manati.star.nesdis.noaa.gov/ascat_images/cur_25km_TEST/zooms/WMBds16.png 

You can do this with any email access from your boat, or from home. We need to keep track of download fees when underway, which could be tied to file size or air time, depending on your system, SSB or sat phone.

You can do this with any of the scatterometer data fields that are available at the site listed, but for offshore use you need to plan this ahead on some level so you know the file names that will cover your route.

The difference between the Saildocs system and what we once offered is you did not need to know the file names. On the other hand, with this one you can get any of the products, whereas for now we offer just the 25-km resolution of ASCAT (metop A).







1 comment:

Werner said...

I tried the above for WMBds221 (Indian Ocean) and I received an error