MTP tutorial

NASA funded the development of the first MTP in 1978 for the study of Clear Air Turbulence (CAT). This development effort was done at JPL under my direction with the engineering support of Richard Denning. For the first 20 years of this effort I was the PI of the MTP program, and since my retirement from JPL in 1998 Dr. Michael J. Mahoney has led the MTP program. I now work only a few hours a week as a consultant for Dr. Mahoney.

During the entire 25-year MTP history several instruments were constructed and used for NASA airborne studies of the atmosphere. For example, MTP instruments have been included on all of NASA's airborne studies of the "ozone hole" beginning with the first one in 1987. To date, MTP instruments have flown aboard 7 aircraft (CV-990, C-141, ER-2, DC-8, WB-57, L118C, M55), on 46 atmospheric research missions, comprising 739 flights for an accumulated 4175 flight hours.

Since Dr. Mahoney is approaching retirement age himself, and since the NCAR use of an MTP instrument appears to be the only legacy for MTP technology, I am preparing this web page as a resource for those at NCAR who might want to learn some of the remote sensing concepts on which the MTP is based. A faster-paced version of this tutorial ("Tutorial on Airborne Radiometry for Aviation Safety Applications") was first written in 1991 for Rockwell International, Collins Air Transport Division, under a contract with JPL for the joint development of an airborne CAT warning and avoidance system based on the MTP concept. The collaboration ended after Rockwell engineers developed an advanced Doppler weather radar for commercial airplanes that was able to obtain clear air signals a short distance ahead of the aircraft. Apparently this system did not work as well as expected for CAT warnings, so maybe there still is merit in considering the MTP approach for an airborne CAT system. In any case, the MTP has become such a useful instrument for atmospheric research studies that the resurrection of the original Rockwell tutorial is still needed. This is especially true since Dr. Mahoney, Richard Denning and I are currently the only three people with MTP experience, and in a few years all of us will be retired.

I will adhere as much as possible to the structure of the original 1991 Rockwell tutorial since nothing about the underlying concepts for MTP have changed. I will try to improve its writing style, and where appropriate I will add comments about recent improvements in analysis techniques and new atmosperhic research uses. I have often stated that the MTP is just another radio telescope, and anyone with an observing background in radio astronomy would immediately grasp concepts underlying the MTP and could become proficient in its use (as Dr. Mahoney demonstrated).

I won't present functional diagrams of microwave components, and there is no discussion of electronics. I leave that for Dr. Mahoney or Richard Denning. My principal task is to describe the remote sensing concepts that led to the MTP's creation in a way that would permit anybody with a bachelor's degree in the physical sciences, and maybe some radio astronomy experience (which is all I had when I developed the MTP) to re-invent the MTP, should that become necessary.

I will use a chapter organization structure. The following links connect you to the chapters:

    1. Fundamentals of thermal radiation - blackbody Planck function
    2. Fundamentals of thermal radiation - antenna temperature
    3. Fundamentals of thermal radiation - brightness temperature
    4. Atmospheric emission when physical temperature is non-uniform
    5. Atmospheric absorption sources and spectrae
    6. Simplest possible retrieval procedure of Altitude Temperature Profile
    7. Backus-Gilbert Retrievals
    8. Statistical Retirevals
    9. Stratified and Other Variants of the Statistical Retrieval Procedure
10. Fundamental Ambiguities for All Retrieval Procedures