OVERVIEW OF THE DC-8 MICROWAVE TEMPERATURE PROFILER

   Figure 1.  Real-time display of MTP retrieval of T(z).

This is an example of a real-time display of JPL's Microwave Temperature Profiler (the MTP/DC8).  It is a plot of temperature versus pressure altitude (km on the left, kft on the right).  The yellow trace is a spline fit to the dots, which are MTP-retrieved air temperature versus altitude, T(z).  The DC-8 is at 11.9 km (39 kft), indicated by a horizontal line segment going though T(z) and yellow triangles at both borders.   The tropopause is at 12.5 km (41 kft), indicated by a shite dashed line and dark triangles at both altitude borders.  Another white dashed line slopes to the lower-right from the tropopause, and denotes the -2 [K/km] criterion for defining a tropopause.  The green area is where nitric acid will condense to NAT clouds, or Type I PSCs (assuming a typical winter mixing ratio profile for HNO3).  The blue area is where water vapor should condense to ice crustals, or Type II PSCs (assuming a water vapor mixing ratio of 4.5 ppmb).

The text information box (upper-right) summarizes 1) aircraft altitude, temperature and potential temperature at flight level, 2) the same properties at the tropopause altitude, 3) the same properties at the altitude of a second tropopause (if one exists), and 4) these properties at the coldest altitude.  The text information box in the lower-left corner is UT corresponding to the time the DC-8 will fly through the air sampled by the MTP (which is typically 15 seconds after the measurement time), the aircraft's flight level [100 foot units], the "flight level of the tropopause, the altitude of the tropopause [kft], and the difference in altitude of the tropopause and the DC-8 [kft].

The bottom line shows aircraft altitude [feet], pitch and roll (deg], latitude and longitude [deg], heading, region number (used in the rretrieval procedure), DC-8 navigation system's outside air temperature, OAT [K], differences between the MTP-based OAT and the navigation system's OAT for Channels 1, 2 and 3 [K], wind speed and direction, MTP-based vertical gradient of air temperature [dT/dZp] for a 1-km layer centered on aircraft altitude, and a symbol denoting whether the altitude and temperature scales and offsets are determined automatically by the real-time program ("a") or by an operator (either "1", "2", or "3").

The MTP/DC8 Installation and Operation

The JPL Microwave Temperature Profiler, MTP, has been successfully relocated aboard the DC-8 in such a way that it can remain on the aircraft without interfering with future mission payloads.  It is now a "turnkey" instrument, and does not require an experimenter for operation.  This means that MTP temperature field data will be available on future DC-8 flights, in real-time, at no cost.  This page describes how MTP data might be useful to other experimenters, and lists limitations without explicit funding of experimenter support. Archived data are available that could be used to produce science-quality temperature fields and other data products if specific flights warrant this and special funding arrangements are made.

What Is the MTP Instrument?

The MTP instrument is a microwave radiometer (i.e., passive) that measures thermal emission from oxygen molecules at 3 frequencies (local oscillator frequencies of 55.51, 56.66 and 58.79 GHz) at a selection of elevation angles.  The MTP retrieves profiles of air temperature versus altitude for a 20-km region approximately centered on the flight altitude.

The MTP sensor unit is located in a window that 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 useable windows that it should not interfere with downstream inlets.  The control and analysis electronics are located in the mission manager's rack, where a dedicated LCD color display shows altitude temperature profiles in the same format illustrated at the top of this web page.

Figure 2.  Mission Manager's desk.  The blue display is the MTP real-time product described in the previous figure.

What Does MTP Display in Real-Time?

The real-time display consists of air temperature versus altitude, 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 less than 2 K (and about 1.0 K from 9 to 16 km) while flying above 11 km.  The display includes a prominent indication of tropopause altitude, both graphically and in a text information table. When a second tropopause is present, as occurs near jet streams, it also is indicated graphically and in the text 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.  The altitude and temperature scales are automatically zoomed-in to show temperature structures close to flight level when this is appropriate, or zoomed-out (surface to 24 kin) when double tropopauses are present.

Data Products Not Included in Real-Time Display

Past MTP scientific results have been based on post-flight data products, and these are only available for missions in which someone from JPL is a funded investigator.  These products include 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 mountain waves, lenticular clouds, mesoscale temperature fluctuation statistics, and tropopause folds, 4) lapse rate monitoring, 5) clear air turbulence, CAT, prediction and avoidance, and 5) selected T(z) plots to support a variety of studies, such as filment encounters, jet stream crossings, anvil sampling, and suspected PSC events.

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Return to home page and click on the link associated with this thumbnail, "Ozone Hole Mission Support," and you'll see another web page with links describing many MTP results on behalf of the NASA ozone hole missions.

This site opened:  September 8, 2000.  Last Update:  June 23, 2007