Computer Modeling Laboratory 7

Written report due: 25 October

Passive microwave remote sensing: retrievals of total precipitable water and cloud liquid water

Lecture 15


In this task you will analyze ground-based passive microwave remote sensing. A ground based upward-looking microwave radiometer has two channels: 23.8 GHz and 31.4 GHz. Consider that absorption by O2 results in optical depths of 0.02 and 0.03 in these channels. Water vapor absorption coefficients are kω are 0.0052 m2/kg and 0.0021 m2/kg, and liquid water (cloud drops) absorption coefficients are 0.087 m2/kg and 0.15 m2/kg. Consider a mean atmospheric temperature T=280K.

  1. What brightness temperature Tb should each channel observe in a perfectly dry atmosphere (i.e., no water vapor or clouds)?
  2. Repeat your calculations with the addition of water vapor having a total water vapor amount (i.e., total precipitable water) of 60 kg/m2. Consider cloud-free conditions
  3. Repeat your calculations again, this time assuming the addition of cloud liquid water with a liquid water path of 0.3 kg/m2, which is typical of a fairly thick nonprecipitating stratocumulus clouds.
  4. Derive a retrieval algorithm for the estimation of total water vapor path amount. Your final algorithm should have the form u= a1*log(T-Tb,1) + a2*log(T- Tb,2)+a3. Need to derive expressions for coefficients a1, a2, and a3.



The NOAA MSPPS (Microwave Surface and Precipitation Products System) project is dedicated to the retrieval of operational surface and precipitation products (including total precipitable water (TPW) and cloud liquid water (CLW)) using a passive microwave sensor AMSU on board of NOAA's polar-orbiting satellites.

A retrieval algorithm for TPW and CLW is described by Grody et al. (2001). Also, a brief description of the algorithms for all retrieved products is available at MSPPS website (see under Algorithms).

Go to the NOAA MSPSS website linked above. Click on the Operational Product Access OSPO link near the bottom of the page.

Click 'Products by Satellite Link' on right side of page.

Select the NOAA-15 satellite.

Select and download the TPW and CLW descending and ascending images.

Download and examine the images. Answer the following questions:

  1. Why wereTWP and CLW not retrieved in the Arctic and Antarctica regions?
  2. Why were TWP and CLW not retrieved over land?
  3. Does the presence of clouds affect retrievals of TWP?
  4. Does precipitation affect retrievals of TWP and CLW? Why or why not?
  5. What are the main sources of errors in retrievals of TWP and CLW?