Date: Mon, 17 May 1999 16:04:21 -0400 (EDT)
From: Rich Fletcher <fletcher@media.mit.edu>
To: mattlau@media.mit.edu, Matthew Gray <mkgray@media.mit.edu>
Cc: Rich Fletcher <fletcher@media.mit.edu>
Subject: weather data decoding
Message-Id: <Pine.OSF.3.91.990517155757.18808C-100000@ml.media.mit.edu>
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Xref: john-muir.media.mit.edu personal.media-lab:1268


Matt, Matt,

     The data from Argos is copied to 2 e-mail lists: argos1 and argos2 
@media.mit.edu.  I recomend using argos1, since I plan to remap argos2 to 
receive another set of ID numbers.

    The e-mail list was locked, but NecSys fixed the problem so you can 
freely add yourselves to the list.

    I'm willing to serve the page offof the phgysics sever temporarily, 
but it should be moved to a server which can handle higher traffic.  Matt 
Gray knows best, so I defer to your judgement.
   BTW, I brought in my large Everest book with an Everest map I want to 
scan for the web site.  

Rich


---------------------------------------

>From Matt Reynolds:

Here is a typical email from one of the probes, received today:
01884 14838   5 13 K B 1999-05-06 13:58:55  27.953   86.853  0.000 401649669
      1999-05-06 14:00:50  2         00           F1           8C           47
                                     FF           01     F18D47FF     FFF18F48
                               FF00F18B     46FF00F1     8A46FF00     F18B46FF
                                   692F

01884 is our Argos administrative account. Probe ID is 14838. 5 13 K B 
indicates that this packet was received by the NOAA-13 satellite. 
We turned on Argos positioning which is very rough (1KM or worse accuracy) and
have the lat/long as 27.953N 86.853E. 

Packets were received at 2pm GMT on 5/6/99. Two identical packets were 
received. 

Now is the tricky part. Look at the last byte in the message. It's 0x2F. This
is the pointer into the message array at which the current hour's data is
placed. The data field begins at 20 and has offsets at 20, 25, 2A, 2F, 34, and 
3F. 2F means the current hour's data is the fourth data set in the message.
The previous three data sets are the data from 1, 2, and 3 hours ago; the
following data set is from four hours ago. (The last byte is a pointer into
the probe's internal data structure)
 
There are five bytes in one hour's data sets. In order, these bytes are 
temperature, battery voltage, pressure, and wind speed. So count out 5 bytes
times the fourth data set which is 20 bytes into the message body. This is
the light level of the current hour and is 0x00 (bright sunlight). 0xF1 is
the battery voltage: 0xF1/0xFF*4.096*3=11.568V. 0x8A is temperature:
0x8A/0xFF*4.096=220.8Kelvin=-52.2C. Pressure is 0x46/0xFF*4.096=Sensor voltage
which in this case is 1.12V.

Then sensor voltage=4.5(Press in KPa*0.009+0.04) so pressure is 23.2KPa. This
probe must be pretty high up, or there was a data error on this packet.

I'd really like to know where those probes went!

Regards, will be writing some software to do this ASAP,
Matt