The first-ever Microwave Temperature Profiler, MTP, flew aboard the NASA CV-990 aircraft on January 12, 1979.

At the time of this first flight the instrument was called Temperature Structure Radiometer (TSR).  The TSR consisted of the engineering model of the SCAnning Microwave Spectrometer, SCAMS, which was not needed after the flight model was successfully launched into Earth orbit as a Nimbus 6 satellite instrument. The SCAMS had been used for ground-based T(z) applications prior to its airborne use.  It was adapted for airborne use in order to assess it's ability to predict encounters with Clear Air Turbulence, CAT.

The closest thing to a mission name is "The 1979 Clear AIr Turbulence Flight Test Program" (title of a final report document describing the flight series and submitted to NASA).  The flight series were funded by NASA to test the CAT warning capability of a high-powered 10.6 micron (CO2) pulsed Doppler lidar that was built at Marshall Space Flight Center (MSFC). It was common knowledge that the lidar was not a mature enough technology to be commercially useful in affording CAT warnigns, mostly because the hardware was so large, heavy and difficult to operate.  Nevertheless, NASA had invested such a large amount into the technology that a final test flight series was considered useful to at least document how well the concept of a Doppler lidar worked in terms of warning times and hit/miss/false alarm rates. Since the CV-990 aircraft for the lidar was not completely filled by the lidar, there was room in the airplane, and also in the budget, for other new and promising sensors to be flown along with the lidar. Pete Kuhn's 20-40 micron water vapor IR radiometer was included in the payload because it had shown promise of predicting CAT when it flew on the Kuiper Airborne Observatory (KAO) C-141 aircraft as a vapor burden support instruemnt for the astronomers on the KAO.

The TSR was included on the basis of my marketing claim that CAT might be predicted when the lapse rate became statically unstabe (adiabatic).  It is ironic that during the coarse of these flights it became obvious to me that CAT was more likely when the lapse rate departed the most from the statically unstable adiabatic value, for reasons given below.  This is a case of the usefulness of the sensor being justified by flight experience, even though the underlying argument for its usefulness was completely opposite of reality.

HARDWARE

The TSR was constructed by modifying the SCAMS instrument during a 5-month period after receipt of funding.  It operated at 53.8 and 55.5 GHz (local oscillator frequency, double sideband), but only the 55.5 GHz data was used.  It was programmed to scan through a sequence of 10 elevation angles (-16, -12, -8, -4, 0, +4, +8, +12, +16, +20 degrees), and to take a calibration measurement of an ambient target.  This sequence was completed every 10 seconds, which corresponded to a distance flown of 3.5 km.  The applicable range for the 55.5 GHz channel was 4 km when flying at 35,000 feet.  The TSR provided air temperature information for applicable altitudes (applicable range times sine of elevation angle) throughout the altitude region -3500 feet to +4500 feet.  Near sea level the altitude coverage was -1000 to +1300 feet.

The TSR horn antenna had a half-power beamwidth of 7.5 degrees.  It viewed the atmosphere through a 1-inch thick high-density polyethylene plate mounted in a passenger window frame mounted on the left side.  The horizon view was 70 degrees of azimuth left of the flight direction, corresponding to a horizon view geometry that intercepted the window plate at ~30 degrees.  Views at other elevations were at slightly greater angles than 30 degrees and corrections were applied for window absorption and reflection at each scan position.  Roll corrections were made to the pointing direction every second.

After 6 scan sequences, requiring 1.7 minutes, the precision of antenna temperature measurements at each scan angle was 0.2 K.  The TSR measures lapse rate, defined here as dT/dZ, with an accuracy of ~2 K/km.  The T(z) shape was used to estiamte the altitude of the tropopause when it was nearby, and the T(z) shape was also used to identiy the presence of an inversion layer (IL).  When flying within an IL the lapse rate of the IL was used to generate an alert for possible CAT (the rationale for which is presented below).

FLIGHT SERIES

The flight series consisted of 30 flights, and the TSR was operated on 29 of these (26 used the vertically scanning mode, and 4 used A fixed +114 degree elevation staring mode).  Real time plots showing crude T(z) were displayed on a printed output of a HP 9825 desktop computer mounted in an aircraft flight rack tray.  These displays were used in the later flights to guide the aircraft to inversion layers and also the tropopause, both of which were favored sites for encountering CAT.  A few successful predictions of CAT were issued on the basis of TSR data, once I figured out that IL and tropopause altitudes is where CAT is found.

A copy of a publication describing results of the microwave instrument investigation of CAT can be found at AIAA81

CAT FORECAST RATIONALE

It was recognized in a June 20, 1979 report that I presented at a mission workshop at MSFC that the TSR was capable of predicting CAT encounters as well as a issuing an advisory on evading CAT by a judicious altitude change.  As stated in this report:  "TSR-derived altitude temperature profiles can be used to identify layers of higher static stability, where vertical wind shear can accumulate to higher values, where the energy of vertical wind shear has been noted to created K-H wave motions that occasionally 'break-down,' or feed short-scale components of motion, known as CAT.  Altitude avoidance is based on the hypothesis that CAT is more likely to be found, ironically, in layers of 'static' stability (i.e., 'stable' layers).  Severity forecasting is based on the hypothesis that CAT severity is related to the amount of vertical wind shear energy contained n dynamically unstable layer, which in turn is related to the static stability of the layer that is approaching instability.  Hence, layers having more 'stable' lapse rates are postulated to be sites of potentially more severe turbulence."  This concept has stood the test of time during my subsequent career of CAT studies.

RECOGNITION OF MTP AS NEW ATMOSPHERIC RESEARCH TOOL

In my June 20, 1979 workshop report I concluded with the following immodest statement:  "The successful sensing performance of the Temperature Structure Radiometer, TSR, signifies the arrival of a new airborne atmospheric remote sensing tool which should find many uses in atmospheric research."

This assessment, after the first MTP mission, turns out to be accurate.  At the time of this writing (2003 October) there have been several MTP instruments built and flown on 7 aircraft, supporting a total of 31 missions, making 599 flights and producing 3458 flight hours of data.

ADDITIONAL MATERIAL
 
Additional material on the origins of the MTP concept can be found at:

  Birth of an Idea                     history of the origin of building airborne version of ground-based temperature profiler
  Spaceflight Article on MTP    popular magazine article of first MTP and results of the MTP/ER2 during first "ozone hole" mission
  MTP Beginnings                    overview of ground-based and all subsequent airborne microwave T(z) instruments

This site opened:  October 28, 2003.  Last Update:  October 29, 2003