TRMM Precipitation Radar PR

1
TRMM Precipitation Radar (PR)

• Anita Rapp
• AT741
• May 6, 2004

2
TRMM PR

• First spaceborn precipitation radar
• Provides 3-D structure of rainfall
• Quantitative rainfall measurements over land and
  ocean
• Combined with the TMI, it improves accuracy of
  rainfall retrievals
• Improves diagnoses of vertical distribution of
  latent heat release

3
Tropical Rainfall Measuring Mission (TRMM)

• TRMM Sensors
• Precipitation Radar (PR) Microwave Radiometer
  (TMI)
• Visible Infrared Scanner (VIRS)
• Lightning Imaging Sensor (LIS)
• Clouds Earths Radiant Energy System (CERES)
• Launched Nov. 1997
• 350/402 km circular precessing orbit at 35º
  inclination

4
PR Characteristics

• Frequency - 13.8 GHz (2 cm)
• Resolution 4.3km horizontal, 250 m vertical
• Swath width 215 km ( 17º scan angle)
• Observes surface to 20 km
• Sensitive to rain rates of 0.7 mm/hr

5
PR Characteristics

• Antenna
• Phased array system with 128 elements
• Beamwidth - 0.71º
• Transmitter/Receiver
• Peak Power 500 W
• Pulse width 1.6 ?s
• PRF 2776 Hz (64 samples)

6
PR Rainfall Retrieval

• Identify hydrometeor type and choose initial
  coefficients between rain rate and Ze from DSD
  model
• Apply attenuation correction, get new
  coefficients relating Ze and rain rate, and
  calculate new Ze profile
• Calculate PIA and correct for non-uniform
  beamfilling
• Use modified PIA to get final Ze profile
• Rain rate is calculated from Z-R relationship
  where the coefficients are initially chosen from
  DSD model, but is modified to maintain
  consistency with new Ze profile and PIA

7
PR Data Products

• Return power
• Noise
• Apparent reflectivity (no attenuation
  correction)
• Attenuation-corrected reflectivity and rainrates
  
• 3-D rain maps
• Rain characteristics convective/stratiform,
  brightband height, storm top

8
PR Limitations

• Narrow swath width
• Attenuation
• Temporal sampling
• Footprint size often larger than rain cell
  (nonuniform beamfilling)
• Limited to Tropics

9
Sample PR images
10
Sample PR imagesTropical Storm Erika
11
Sample PR images
12
Sample PR images
13
Sample PR Long Term Rain Map