Description and Interpretation of ARM satellite Imagery (Hovmuller
Diagrams)
The Satellite Imagery
Each satellite image consists of four infrared channel and one visible
channel full disk images. The full disk images are gridded into 5 km
resolution
pixels and the region 120 E, 10 N and 180 E, 10 S (1336x448 pixels)
extracted.
The extracted image consisting of all four IR channels and visible channels
is then saved as a HDF format file and is available from the archives.
Hovmuller diagrams are created from these images to enable a quick overview
of conditions over an ARM site as well as to assess the availability of
imagery for a particular hour.
Hovmuller Diagrams
A Hovmuller diagram is a plot of Latitude or Longitude variation with
time.A latitudinal 
Hovmuller
diagram for instance shows variation of a parameter with latitude and time.
In the case of satellite imagery a strip of 40 pixels over a TWP site
is extracted for the IR and Visible GMS images available. These strips of IR
and Visible pixels
for each
image are then stacked over each other to create a image for each day.
These daily Hovmuller images would then allow an investigator:
1) To verify the availability of satellite imagery for a particular day
2) The cloud cover conditions over a particular location during a time
period
Interpreting Example Image for Availability
The example image contains the IR and visible longitudinal strips over Manus
for Julian day 080 in
1992. The black strips in the images at 13, 14, 20 and 21 hours show that
there were no images
for these hours.
Interpreting Example Image for Conditions
The dark green spot at 04 GMT (13 LST) over the Latitude of -2.0N
in the IR channel shows that a very cold cloud was
generated over that location. That the cloud was thick as well is shown by
the high albedo as depicted by light mauve color over the same location
in the visible image. These two criteria point that the cloud was most
possibly a deep convective cloud.