Global Precipitation Monitoring - Satellite-based Applications on Climate Change - page 81

Table 6.1 Summary of satellite methods for the retrieval of precipitation
Observation
spectrum

Satellite
type

Sensor
examples Strength Weakness

Visible (VIS) GEO GOES

Imager

Cloud type Cloud tops

LEO AVHRR Cloud evolution Indirect rain rate

Infrared (IR) GEO GOES

Imager

Cloud temperature Cirrus contamination

LEO AVHRR Cloud evolution Indirect rain rate

Passive microwave
(PMW)

LEO SSM/I Direct measure of rain,

especially over
ocean

Poor temporal
sampling

AMSR-E Coarse spatial

resolution

TMI Indirect rain rate (land)

Active microwave
(AMW)

LEO TRMM PR Direct measure of

vertical structure
of rain

Narrow swath width

CloudSat
CPR

Poor temporal
sampling
Rain rate sensitivity/
saturation

has emerged which attempts to utilize the strengths of both wavelengths (e.g., Ba
and Gruber 2001 ).
To illustrate the spatial coverage and information content available from IR
satellite measurements, Fig. 6.1 gives a multi-satellite (i.e., numerous GEO and
LEO satellites) composite of IR imagery from 1500 UTC, 2 June 2010. This data is
freely available from the Naval Research Laboratory (NRL) in Monterey, CA, at
http://www.nrlmry.navy.mil/sat_products.html . If one looks closely at this IR com-
posite, the cloud patterns associated with midlatitude cyclones are quite evident by
the large, bright features that correspond to high-level clouds. On the other hand,
the tropical regions are dominated by cloud clusters corresponding to tropical
convective features that are associated with the Intertropical Convergence Zone
(ITCZ). The darker clouds are lower level clouds, typically associated with stratus
clouds which may or may not be associated with rainfall. A comparable VIS image
(not shown) would show other information but would be restricted to approximately
a 180 longitudinal zone where sunlight is reflecting off the cloud tops.

6.2.2 Passive Microwave Methods

Unlike VIS and IR signals, microwave (MW) energy can penetrate clouds, in
particular, cirrus clouds, and its signal has a strong interaction with precipitation-
size drops and ice particles. This direct impact on microwave measurements by
hydrometeors allows for the quantitative detection of precipitation properties in the
atmosphere as well as on the surface. It should be pointed out that passive MW
(PMW) means naturally emitted radiation from the Earth's surface and atmosphere