SGP/MMCR/C1 - Poor cross polar isolation

This last spring, Sergey Matrosov pointed out that the Circular Depolarization Ratio 
measurements on the SGP radar indicated the isolation between the co and cross channels was 
only about 15 dB. Typically isolation of 25-30 dB is expected for polarization measurements 
to be useful.

We set about to see if we could identify the source of the poor isolation. Kevin Widener 
had purchased a custom built orthomode transducer and polarizer  that hadn't gone through 
any previous testing and we decided to swap it out with an ETL unit that had shown good 
isolation in the past. Kevin performed the swap a couple of weeks back and this week the 
latest archive data was available to compare results between the OMTs. 

Results from two precipitating cloud conditions, where we looked below the melting layer, 
where we expect to find domination of spherical water droplets and therefore maximum 
values for cdr  - the maximum isolation (CDR) appears to be about 17 dB. The results showed 
that the poor isolation is probably not due to the OMTs but rather to the antenna itself.

• CircularDepolarizationRatio

SGP/MMCR/C1 - Dual polarization modes discontinued

During a heat spell, the MMCR shelter internal temperature approached 100 F after the air 
conditioner failed. Either the heat, or a UPS failure, caused a failure of the MMCR radar 
computer hard disk. I had a spare computer shipped from Barrow and installed it on 
8.24.2010. I was unable to get the dual polarization modes working. With help from Coy 
Chanders (the software developer) and Ken Moran (the hardware developer), we were able to 
determine the problem was the spare was running an older version of Lap-XM.  

Since the MMCR will be upgraded in two months and the antenna (to be replaced in September 
and its cross-polarization isolation makes cross-polarization essentially worthless), I 
decided to eliminate the dual-polarization modes. Dual polarization will return with the 
MMCR upgrade in October.

The MMCR was removed from service 20110104 to be replaced by the KAZR instrument.

• ModeNum