Computer Modeling Laboratory 8

Written report due: 6 November

Applications of passive remote sensing using emission: Sounding of atmospheric temperature. Retrievals of SST.

RELATED MATERIALS:
Lectures 11 and 12

TASK 1
  1. The concept of the weighting function is the central to the sounding techniques. An example of the real weighing function is shown here.
    1. Explain why the lower and upper parts of the atmosphere have the smallest values of the weighing 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.
  4. The sounding techniques are also actively used in space science. In your opinion, will it be possible to perform sounding of the temperature profile of the Martian atmosphere? If yes, then in what spectral regions?
    HINT: Think about composition of the Martian atmosphere. For more help, look for info on a Mars climate sounder of the Mars Reconnaissance Orbiter (MRO) mission.

 

TASK 2

SSTs are retrieved from remote sensing observations in both IR and microwave regions. For instance, AVHRR and MODIS use the IR window, while the TRMM Microwave Imager (TMI) and SSM/I operate in the microwave. Both IR and microwave retrieval techniques have some inherent advantages and disadvantages.

  1. The IR remote sensing of SST requires the cloud-free conditions. However, the presence of dust (or volcanic aerosols, or thin cirrus cloud) can also affect the retrievals of SST.
    Estimate how SST errors depend on the aerosol optical dept of dust. Consider the dust layer-underlying surface system. Ignore scattering by dust.
  2. Analyze SST retrieved from AVHRR and TMI against buoy data in the Gulf of Mexico. Consider August 2008. Buoy data are provided by, the National Data Buoy Center (NDBC) a part of the National Weather Service that develops, operates, and maintains a network of buoy and C-MAN stations. Consider two sites: #42002 (west side of the Gulf) and buoy #42003 (east side of the Gulf). To get data, type station ID number or select on a map, look for Historical data, and "Standard meteorological data" (buoy sea surface temperature is called WTMP). Download data for both sites.

    Data for AVHRR and TMI (along with all other SSTs) are available from the High Resolution Diagnostic Data Set interactive website http://medserve.noc.soton.ac.uk/mydds/sst/.
    On a map find buoy sites, then for each site, general a plot of SSTs (for August, 2008) and download the data (see link under the plot). Note that you can see the spatial SST by clicking on a particular symbol on the plot. See legend under the plot.
    In downloaded data files, select SST retrievals from AVHRR and TMI/TRMM and compare them against buoy data. Briefly discuss the possible reasons for the differences in SST retrieved from AVHRR, TMI and buoys.
    HINT: look for info on meteorological conditions during August 2008.
    Also see an example here for Hurricane Danielle during August 1998.