Computer Modeling Laboratory 10

Written report due: 20 November

Radar remote sensing of precipitation

Related material:
Lecture 14
S: 8.1-8.3, pp.408-410



Weather radar reflectivities are affected by rain, as well as by several other factors. Read a short tutorial and then take Quiz to test how well you can interpret radar images. Report your answers along with correct quiz's answers.


The National Weather Service operates the radar network to monitor the precipitation. See FAQs for more information.

  1. The radar reflectivity-rain rate relationship (called Z-R relationship) used operationally by the National Weather Service to calculate the rainfall rate is Z=300(Rr)^1.4. Using today's radar data for Georgia, calculate a maximum rain rate.
  2. On a log-log scale, plot Z-R relationships developed for stratiform rain and orographic rain (see Lecture 14). On your plot, indicate rain rates corresponding to radar reflectivities of 40 dBZ and 60 dBZ for these types of rain. Explain the differences. HINT: Think about size spectra of rain drops.
  3. Estimate the errors in retrieved rain rates due to the underestimation of the measured radar signal by a relatively small amount, say 3 dB.



TRMM is the first satellite dedicated to tropical rainfall observations, and is the only satellite that carries a weather precipitation radar. The TRMM satellite has 5 sensors on board, which are Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible Infrared Scanner (VIRS), Clouds and the Earth's Radiant Energy System (CERES), and Lighting Imaging Sensor (LIS).
A brief description of TRMM PR is available here.
Examples of TRMM PR and TMI of cyclones are available here.
Although the space radar offers several unique capabilities for observing precipitation, radar retrievals still have some critical shortcomings. Read a short paper describing the most recent improvements of TRMM PR retrievals of precipitation.
Answer the following questions:
1) Briefly discuss advantageous and disadvantages of measuring precipitation with a space radar, and contrast to passive microwave remote sensing (e.g., TRMM TMI).
2) What are the main sources of errors in precipitation retrievals from TRMM PR?
3) What are the main challenges in validation TRMM PR precipitation data?
4) A future Global Precipitation Mission (GPM) will include a Dual-frequency Precipitation Radar (DPR). Briefly explain the need (advantages) of adding the second frequency.