Origin of DMSP 1.9-second flashes

Ed Cannon (ecannon@mail.utexas.edu)
Sat, 06 Sep 1997 15:15:42 -0500

Tristan Cools <tcools@nic.INbe.net> asked regarding 1.9-second period
flashes exhibited by more than one DMSP satellite:

>Any idea were those flashes are comming from ?  
>
>I have checked the PPAS database and found two other DMSP Block 5D--2
>satellites with the same flash period of 1.9s:

I believe that I have found the answer.  This is from the "Defense 
Meteorological Satellite Program Technical Review" at:

   http://psbsgi1.nesdis.noaa.gov:8080/EBB/pubs/sympos/symp2.html

> "2. DMSP ELECTRO-OPTICAL AND MICROWAVE SENSORS"
>
> "2.2. Special Sensor Microwave Imager (SSM/1) - The SSM/I instrument 
> measures the microwave radiation from the earth's atmosphere and 
> surface. ...
>
> ...  All satellites through S-15 will fly a microwave imager, except 
> for F-9.  ...  The sensor conically scans the earth at a rate of 
> 31.9 scans/minute. 
>
> ...
>
> The SSMIS has a two point (hot and cold load) calibration, taken once 
> each scan of 1.9 seconds in all 24 channels. 

The satellites are 3-axis stabilized, so apparently we're seeing 
reflections off a rotating scanning mechanism!

Ed Cannon
Austin, Texas, USA
30.3086N, 97.7279W, 165m