Computer Modeling Laboratory 8

The concept of the weighting function play a key role in atmospheric sounding. This task will help you to develop a better understanding of the nature of the weighting function.

1. An example of the actual weighting function is shown here.
   1. Explain why the lower and upper parts of the atmosphere have the smallest values of the weighting function. Check your explanation here.
   2. The altitude at which the peak of the weighting function occurs depends on the strength of absorption for a given channel.
      The channels located in the center of an absorbing line peak high in the atmosphere. Briefly explain why?
      The channels located in the wings of the absorbing line peak low in the atmosphere. Briefly explain why?
2. The High Resolution Infrared Radiation Sounder (HIRS) is a sounding instrument that provides important information on the vertical profile of atmospheric temperature in cloud-free conditions. HIRS has been the primary source of atmospheric sounding data from NOAA satellites since first flown on TIROS-N (Television InfraRed Operational Satellite-N) in 1978.
   1. This plot shows the NOAA-14 HIRS Spectral Response Functions superimposed on a calculated, high-resolution brightness temperature spectrum for the cloud-free condition. Which of HIRS channels can be used for retrievals of temperature? Which of HIRS channels can be used for retrievals of water vapor? Briefly explain why.
   2. This plot shows the transmission calculated for some NOAA-14 HIRS channels. Sketch the weighting functions for channels 2, 10, and 12 and briefly explain their behavior.
3. AMSU (Advanced Microwave Sounding Unit) is a new microwave sounder that also flies on the NOAA satellites. This table compares the channels of AMSU-A with other microwave satellite instruments
   1. Which AMSU-A channels can be used for the temperature profile retrievals? Briefly explain why.
      HINT: look at the microwave spectrum
   2. Comparing two AMSU-A channels 3 and 8, which channel has the weighting function with a higher peak in the atmosphere? Briefly explain why.

The Atmospheric Infrared Sounder (AIRS) is an advanced sounder containing 2378 infrared channels and four visible/near-infrared channels, aimed at obtaining highly accurate temperature profiles within the atmosphere plus a variety of additional Earth/atmosphere products. In combination with the Advanced Microwave Sounding Unit (AMSU) and the Humidity Sounder for Brazil (HSB), AIRS constitutes an innovative atmospheric sounding group that provides accurate temperature and humidity profiles throughout the atmosphere with global coverage twice daily (day and night) on a 1:30pm sun synchronous orbit. AIRS provides high accuracy retrievals of temperature; however, biases occur in the presence of dust or cirrus clouds that are difficult to correct for in the retrieval algorithm.

In this task you will analyze AIRS spectra taken on 23 July 2006, off the west coast of Africa. See MODIS true color image and aerosol optical depth collocated with AIRS pixel here. Using AIRS spectra compute brightness temperature and determine changes (biases) in brightness temperasture caused by dust.

AIRS data