START-08 NGV Microwave Temperature Profiler (MTP)

Instrument:
HAIS NGV Microwave Temperature Profiler (MTP)

Principal Investigator:
Michael J. ("MJ") Mahoney

Co-Investigator:
Julie Haggerty, NCAR

Organization:
Jet Propulsion Laboratory
Mail Stop 246-102
4800 Oak Grove Drive
Pasadena, CA 91109-8099

Phone:             (818)-354-5584
FAX:                (818)-393-0025
E-mail:             Michael.J.Mahoney at jpl.nasa.gov
URL:                http:\\mtp.jpl.nasa.gov\

MTP (above) is located on the GV's right outboard wing strut.

Principle of Operation and Data Products

The NGV (formerly HIAPER) MTP is a passive microwave radiometer, which measures the natural thermal emission from oxygen molecules in the earth’s atmosphere for a selection of elevation angles between zenith and nadir by scanning through an arc in the flight direction. The NGV observing frequencies are 56.363, 57.612 and 58.363 GHz. These frequencies are different from our other instruments because the NGV MTP makes measurements centered on the oxygen absorption lines rather than being centered between oxygen absorption lines. We expect this to improve the overall performance. The measured "brightness temperatures" versus elevation angle are converted to air temperature versus altitude using a quasi-Bayesian statistical retrieval procedure. An altitude temperature profile (ATP) is produced in this manner every 15 seconds (about 3 km) along the flight track.

An example of an MTP realtime altitude temperature profile (ATP) obtained aboard the DC-8 during the SONEX campaign is shown to the right. The yellow dots are retrieval levels, the horizontal white dashed line is the tropopause altitude. A similar display will be available aboard the NGV during START-08.

Color-coded Temperature Curtain

ATPs can be used to produce a color-coded temperature curtain (CTC) of the temperature field which the NGV has flown through, which can be used to provide meteorological context for measurements made by in situ and remote sensors of atmospheric gases, hydrometeors and aerosols. In addition, the temperature field can used to determine the tropopause altitude, which is extremely important to interpreting other measurements, especially on a campaign like START-08 which is focussed on studying the UTLS.

A CTC is shown in the figure to the right for a transit flight from Alaska to Hawaii. The DC-8 altitude is shown as the black trace, and the tropopause altitude by white dots. The tropopause height jump at both the sub-tropical and polar jets are obvious, and there is an extended region north of latitude 38 North where a double tropopause exists.

Isentrope Cross-section

The temperature field can also be converted to a potential temperature field so that isentropes can be identified. This is very useful for studying atmospheric dynamics such as meso- to synoptic-scale atmospheric waves. The "waviness" of isentropic surfaces is used to characterize the magnitude of temperature fluctuations, which is needed for deriving effective temperatures to be used in atmospheric chemistry calculations involving reaction rates and solubility.

An isentrope cross-section for a SOLVE flight over the Norwegian Mountains on January 25, 2000, is shown to the right. The green area shows the east-to-west terrain cross-section, while the black traces show MTP isentropes and the blue trace, the DC-8 flight altitude.

Hardware Description

As is shown in the figure at the top of the page, the NGV MTP is mounted in a standard 7"-diameter PMS cansiter. A block diagram of the MTP hardware is shown to the right. As shown on the left of this figure, most of the MTP components will be located inside a fiberglass Fairing (2) on the front of a seven-inch-diameter aluminum Canister (1). The fairing will contain a HDPE Window (3) for viewing using a Scan Mirror (5) inside the fairing, which is driven by a Stepper Motor (6). In addition to viewing ten different elevation angles from near-zenith to near-nadir in the flight direction, the Scan Mirror also views a Reference Target (4) for gain calibration purposes. The RF signal received by the Scan Mirror connects to the Radiometer (7), which is mounted on a thermally isolated temperature-controlled plate. A microwave signal from a Frequency Synthesizer (9) is fed into the Radiometer to down-convert the RF signal to baseband. The Frequency Synthesizer and Power Supplies (10) are located in the Canister itself, which is mounted on a wing hard point strut.

The detected baseband signal is sent to the Controller Board (8), where a voltage-to-frequency converter (VFC) produces counts proportional to the detected signal power. The Controller Board also communicates with the MTP Cabin Computer (MCC). The Controller Board also receives and processes commands from the MCC and sends data back to the MCC. The MCC will record this data and retrieve real time temperature profiles. The raw data will also be recorded on the ADS3.

Small PIC-based Temperature Controller Boards are used at four locations in the MTP to maintain stable temperatures and to prevent condensation on descent after cold soaking. These locations are the Reference Target, the Radiometer Plate, Power Supply/ Synthesizer Plate, and the Controller Board enclosure. The controllers all operate near 40 C.

MTP/ER2 Performance

Accuracy:

Response Time:

Vertical Resolution:

Temperature accuracy is approximately 1 K within 3 km of the NGV flight altitude, and < 2K for an 6 km region centered on the NGV.

In practice over the past few years, we have obtained a temperature accuracy of <1 K as far as 10 km from flight level. This is illustrated in the image to the right showing performance during the CRAVE campaign on the WB-57F.

15 seconds per temperature profile

150 meters at flight level, and approximately half the distance from the aircraft away from flight level.

For more information, go to the MTP Home Page ( http://mtp.jpl.nasa.gov/ )