30
C.L. Gentemann et al.
Table 2.4 Sources of RFI
Source
Region affected
Frequency
(GHz)
Effect on data
(↓ decreases)
Affected
overpass
Period of
interference
HotBird
Europe
10.7
↓ SSTs
↑ Winds
Descending
Pre 2002 –
present
Astra
Europe
10.7
↓ SSTs
↑ Winds
Descending
Pre 2002 –
present
Atl.Bird 4A Mediterranean
10.7
↓ SSTs
↑ Winds
Descending
April 2009 –
present
DirecTV-10 USA
18.7
↓ SSTs
↑ Wind
↓vapor
↑cloud
↑rain
Descending
September
2007 – present
DirecTV-11 USA
18.7
↓ SSTs
↓ Wind
↓vapor
↑cloud
↑rain
Descending
July 2008 –
present
SkyBrazil
SE American Coast 10.7
↓ SSTs
↑ Winds
Ascending
Pre 2002 –
present
Groundbased
Ascension Island
6.9
↓ SSTs
No wind effect
Both
Pre 2002 –
present
Groundbased
Gulf of Aden
10.7
↓ SSTs
↑ Winds
Both
March 2009 –
present
Groundbased
Coastal Netherlands
Coastal Norway
6.9
↑ SSTs
No wind effect
Both
2004 – present
Groundbased
Mumbai
6.9
↑ SSTs
No wind effect
Both
2003 – present
years. Ground-based RFI sources can operate intermittently, sometimes even sporadically. The most prominent regions include coastal Netherlands and Norway,
coastal Mumbai, the Gulf of Aden through the waters south of Oman, and waters
around Ascension Island.
Regions of RFI are located by differencing AMSR-E SSTs derived using all SST
channels (6.9–36.5 GHz) from those derived without 6.9 GHz (10.7–36.5 GHz), as
well as by differencing winds derived using all wind channels (10.7–36.5 GHz)
from those derived without 10.7 GHz (18.7–36.5 GHz). An example is shown in
Fig. 2.6.
Since most geostationary sources affect the AMSR-E descending passes, this
plot shows the wind (North America) and SST (Europe) descending orbit difference
maps. The wind RFI around North America caused by DirecTV outlines US coastal
waters and the Great Lakes (both pictured), with some subtle effects detected as far
as Hawaii and possibly the Canary Islands off the coast of Africa (neither shown).
The SST RFI around Europe shows consistently increasing extent and intensity over
the years.