Instrument
Description: The JPL Microwave Temperature Profiler (MTP) is
a passive microwave radiometer that measures the natural thermal emission
from oxygen molecules at three frequencies (55.51, 56.66 and 58.79 GHz).
The instrument views ten elevation angles between - 80 and +80 degrees
by using a scanning mirror -- located behind a microwave window on the
sensor unit -- to change the viewing direction. As shown in the figure,
the sensor unit is located in a window just aft of the forward starboard
exit door. This window has always been considered inaccessible for science
instruments or inlets because it is immediately behind the Mission Manager's
console. The sensor fairing is far enough ahead of other usable windows
that it should not interfere with any future sampler inlets. The control
and analysis electronics for the MTP are located in the Mission Manager's
rack. The MTP retrieves profiles of air temperature versus altitude, which
it displays on a dedicated color LCD display beside the Mission Manager's
console; a video signal is also available for distribution to DADS monitors
throughout the aircraft.
What Does MTP Display in Real-Time? The real-time display consists of air temperature versus altitude, from near the surface to 24 km, and is updated every 17 seconds. Simulations, and comparisons with radiosondes, show that RMS performance is better than available from synoptic-scale analyses (such as NMC) throughout the altitude region 6 to 18 km, where MTP exhibits an RMS of <2 K (and <1.0 K from 9 to 16 km) while flying above 10 km. The display includes a prominent indication of tropopause altitude, both graphically and in a text information box overlay. When a second tropopause is present, as occurs near jet streams, it also is indicated graphically and included in the table. A "ghost profile" feature shows T(z) averaged over the past 4 minutes, which is useful in quickly noting the altitudes where temperature is changing rapidly.
What an MTP Experimenter Provides: Past scientific results for missions on which MTP has been funded have been based on post-flight data products. These products typically included: (1) a standard data exchange file, archived on a mission-specified computer, (2) plots of tropopause altitude versus time (or latitude/longitude), (3) plots of isentrope altitude cross-sections, which are useful in the study of wave clouds, mountain waves, temperature fluctuation statistics, (4) color-coded temperature cross-sections (CTCs), (5) lapse rate monitoring, (6) clear air turbulence prediction and avoidance, and (7) selected T(z) plots to support a variety of studies such as filment encounters, jet stream crossings, anvil sampling, suspected PSC events, and sub- visible cirrus lidar measurements.
If a MTP experimenter is on board the DC8 there are many realtime enhancements that can be provided. First. the normal realtime altitude temperature profile (ATP) display is monitored to ensure it's integrity (by ensuring that appropriate retrieval coefficients are being used) and usefulness (by optimizing the display to show features of interest and by taking advantage of program features not available with the default display.). This is possible because the experimenter can interact with the realtime analysis computer (CAC) via a serial and/or LAN cable that connects to the experimenters laptop. (Image of DC8 layout.) In addition, although thorough post-flight analysis is needed to verify instrument calibration and data integrity, many of the above described data products will be available on GTE PEM Tropics B in real-time. For example, as was demonstrated for the first time on SONEX, realtime color-coded temperature curtains (CTCs) could be displayed over the DADS video system because the MTP experimenter is able to control the video source (default ATP from CAC, or CTC from the experimenters laptop) that is provided to DADS for distribution. Also, for PEM Tropics we expect to provide displays in terms of geometric altitude (instead of pressure altitude) as this is more useful for comparisions with LaRC/DIAL.lidar measurements. This will require however that GPS altitude is available from DADS. We will also use MTP data to integrate the hydrostatic equation and provide number density profiles for more accurate mixing ratio determinations.
