Overview of the TEFLUN A & B field campaigns

The TExas and FLorida UNderflights (TEFLUN) Experiment is a mission to obtain validation measurements for the Tropical Rain Measuring Mission (TRMM). TRMM is a NASA and National Space Development Agency of Japan (NASDA) coordinated mission that launched the TRMM satellite on 28 November 1997 with a unique complement of sensors to remotely observe rainfall throughout the global tropics. TEFLUN is the first in a series of experiments using a combination of airborne and surface-based measurements to complement the satellite data. Among these, are important measurements aboard the NASA high-altitude aircraft, similar to those on the TRMM satellite. They are used for direct intercomparisons with TRMM overflights where possible, but more frequently to simulate TRMM data by flying over precipitation systems within the experimental domain. These, along with in situ aircraft data, surface-based measurements and computer models, will make unique contributions to our understanding of the tropical precipitation spectrum.

TRMM field campaigns (FCs) aim at validation of the ground validation products derived from radars and rain gauges, TRMM-derived Levels 2 and 3 radiometer, rain and rain profile products, and vertical profiles of latent heating. Since latent heating profiles cannot be directly measured, numerical cloud models are used in TRMM algorithms to provide the link between the latent heating profiles, TRMM radar and radiometer observations. Consequently, an important part of the campaign is to provide comprehensive observations of the structure and evolution of Mesoscale Convective Systems (MCS), individual convective events, and their environment. Cloud and mesoscale models require these data sets for initialization and the subsequent model results must be validated for realism of vertical structure and latent heating. While the TRMM instantaneous and monthly algorithms can be evaluated through intercomparison with ground validation (GV) and other data sets, the campaigns will provide additional observations required for a more thorough validation and guidance for improving the algorithms.

• The overarching scientific objective of TEFLUN is to obtain a database suitable for case studies of a few MCSs, early in the TRMM lifetime, from which cloud-resolving models and forward radiative transfer models can be used to understand and improve the performance of the satellite and GV algorithms.
  
  
• Perform underflights of TRMM by the ER-2 and DC-8 with high-resolution radar and passive microwave instruments to assist in evaluating the effects of resolution and sensitivity on algorithms using the Precipitation Radar (PR) and TRMM Microwave Imager (TMI) data. (Since underflight opportunities are limited, similar flight lines to simulate TRMM data should be performed over precipitation targets more frequently.)
  
  
• Evaluate and improve algorithms using ground-based radar data [i.e., GV algorithms] for estimating rain rates, vertical profiles of hydrometors, and separation of convective and stratiform precipitation regions by using a combination of augmented ground-based measurements and aircraft overflights.
  
  
• Provide guidance for improving the assumptions in algorithms using TRMM satellite data as inputs to estimate rainfall and latent heating profiles, particularly the ones which involve microphysics, i.e., vertical distribution of hydrometeors.
  
  

TEFLUN-A will be conducted between April 1 and May 15, 1998, principally focused on the Texas ground validation site. The NASA ER-2 aircraft participation is planned for April 8 - May 8, 1998 based at Eglin AFB, FL. A cloud physics aircraft based within or near the TX site will also participate. There is close coordination with the Houston and other WSR-88Ds, the Texas A&M ADRAD Doppler radar, the NOAA ETL X-band polarization radar (X- POL), and the NOAA AL Profiler system. These ground-based facilities are integrated with dense rain gauge networks and disdrometers. Soundings will be obtained from two mobile systems to provide initialization and validation data for models at strategic times and locations.

TEFLUN-B will be conducted between 1 August and 30 September 1998, principally focused on the Florida ground validation site. ((DC-8 actually arrives around the 10th)) It will be conducted in close coordination with the 3rd Convection And Moisture Experiment (CAMEX-3), both involving NASA ER-2 and DC-8 aircraft, and a cloud physics aircraft, all based at Patrick AFB, FL. There is close coordination with the Melbourne and other WSR-88Ds, the NCAR S-band polarization radar (S-POL) radar, the array of facilities at the Kennedy Space Center, and the NOAA AL Profiler system. Soundings will be obtained from two mobile systems to provide initialization and validation data for models at strategic times and locations. A dense network of ground-based facilities measurements will also be utilized in TEFLUN-B.

The ER-2 and the DC-8 during TEFLUN-B, will carry instruments associated with TRMM objectives. The instruments most relevant to TRMM are a subset of the payloads carried by each aircraft.

ER-2 Doppler Radar (EDOP)

Advanced Microwave Precipitation Radiometer (AMPR)

Lightning Instrument Package (LIP)

Multispectral Atmospheric Mapping Sounder

Millimeter Imaging Radiometer

Airborne Rain Mapping Radar

Polarimetric Scanning Radiometer

Airborne Multichannel Microwave Radiometer

Cloud/Aerosol Particle Characterization

Dropsondes

There are several additional instruments that will be flown on the DC-8 as part of CAMEX-3. These instruments will provide valuable information for the TRMM objectives.

More detailed descriptions of the full ER-2 and DC-8 instrument complements TEFLUN-B/CAMEX-3 are given on the TEFLUN-A/B and CAMEX3 web sites:
TEFLUN-A/B: http://cloud1.arc.nasa.gov/teflun
CAMEX-3: http://www.ghrc.msfc.nasa.gov/camex3

Surface-based facilities which will form part of the database for TeFLUN-B incllude the Melbourne and other WSR-88Ds, the NCAR S-band polarization radar (S-POL), the array of facilities at the Kennedy Space Center, and the NOAA AL Profiler system. These ground-based facilities are integrated with dense rain gauge networks and disdrometers. Soundings will be obtained from the two mobile systems. The enhanced surface network for TEFLUN-B is shown in the following figure:

In addition to the enhanced TEFLUN-B surface network near the S-POL radar, the TRMM Florida GV network with the WSR-88D's will also be used as part of the flight region for the aircraft. This network covers most of Florida.

A more detailed description of the TEFLUN-B GV network can be found at the TRMM Office web site:
http://trmm.gsfc.nasa.gov/trmm_office/field_campaigns/teflun/teflunb/teflunb_gv.html

• NCAR S-Band polarimetric radar

  Overview:

  In 1996 the Natiional Center for Atmosphereic Research (NCAR) began a program in radar hydrology and in particle discrimination. Hydrological goals are to improve Z-R relationship technology for estimating precipitation and to evaluate the potential of dual-polarization measurements for estimating precipitation. Other programmatic goals seek to develop techniq;yes for the remote detection of precipitation particle types (raindrops, snow crystals, graupel, and hail).

  The corner stone of the program is NCAR's S-band, dual-polarization radar (S-POL). Measureables include radar reflectivity, differential reflectivity, differential propagation phase, the correlation coefficient between reflectivity an hoizontal and vertical polarization, the linear depolarization ratio, and the radial velocity. More details concerning the radar can be found at:
  Http://www.atd.ucar.edu/rsf/spol/spol.html

  Operations and Realtime Products:

  S-Pol will be located at longitude 80° 44.736 min and latitude 27° 53.360' (200° and 26 km from the WSR-88D at Melbourne) and will operate from approximately 20 July until 30 September 1998. Operations will be conducted whenever precipitation is observed or forecast within the S-Pol umbrella. It is expected that a large number of hydrologic events will be collected. In addition S-Pol will support TRMM activities. A number of realtime products are available. Precipitation estimates (maps) are generated from radar reflectivity, specific differential phase, a combination of differential reflectivity and reflectivity, and from a combination of all three polarimetric variables. Accumulation times can be as short as ten minutes and as long as storm duration. There is a realtime hail detection algorithm. A recent addition is a particle discrimination product which will make designations in eleven categories.

  Scanning Strategies:

  For hydrological experiments S-Pol will be operated in full PPI or sector mode. A number of experiments are planned:

  1. NEXRAD mode: For some experiments the radar will be operated at elevation angles of 0.5, 1.45, 2.4 and 3.35°. This strategy permits duplication of precipitation products with the WSR-88D.
  2. Continuous sammpling: In this mode the radar will operate continuously at a constant low elevation angle ( most likely 0.5°). The purpose is to determine the benefits of more frequent temporal sampling. The likely sampling interval is 55 sec.
  3. Three-dimensional mode: The radar will operate in a fixed sector mode over a concentrated network of gages. The measurements support neural network approaches to rainfall estimation.
  4. Doubled sampling: Normally 60 samples are collected at each polarization. For some experiments the radar will be operated in sector mode with double the number of samples.

  The radar can be operated in either sector or vertical cross-section modes. Antenna speeds are 6.5°/sec in sector mode and 3-4°/sec in RHI mode. Data collections are flexible in terms of sector and elevation limits. Some examples with approximate scan durations are:

  1.   60° azimuthal sector with 20 elevation angles: 3 min 20 sec
  2. 120° azimuthal sector with 15 elevation angles: 5 min
  3. 180° azimuthal sector with 15 elevation angles: 7 min 20 sec.

  An RHI scan for an azimuthal sector of 30°, with elevation angles from 0 to 40°, and an azimuthal increment of 1° will take 6 min 40 sec at an antenna speed of 3°/sec and 5 min at 4°/sec. Full RHI's (horizon-zenith-horizon) are not possible. A proxy can be accomplished by stringing two RHI scans with elevation angles of 0 to 85° and a null sector width. Such a scan will take approximately 1 min 15 sec to complete.

• NOAA/AL Doppler radar profilers
  (see above)
  
  
• IIHR Mobile Rainfall Observatory

  The Iowa Institute of Hydraulic Research (IIHR) of the University of Iowa, operates the so-called Mobile Rainfall Observatory, which includes a trailer-based vertically pointing X-band radar (owned jointly with the Hydrologic Research Center of san Diego, California), a 2-D video disrrometer, dual-design tipping-bucket raingages, and other surface meteorological instruments. The instrumentation is described below. Pictures of the instrumentation appear on the web at:
  http://www.iihr.uiowa.edu/trailer/

• Vertically Pointing Radar

  The basic specifications of the vertically pointing radar are shown in Table 1. The radar was built at the McGill Radar Weather Observatory, McGill University, Canada. The microwave part of the radar is essentially a widely-used navigation radar manufactured by Decca. It is controlled by a PC equipped with a PCIP-SCOPE digital oscilloscope card, maunfactured by Keithly Metrab;yte, and software written by the developers of the radar at McGill University. The radar data acquisition software provides a rudimentary display program that is useful for confirming operation of the radar. Additional C library routines that enable reading, plotting, converting the data to a format that is easier to distribute, and analyzing the data, has been developed at IIHR. Recently, the radar was upgraded to Doppler capability using a PIRAC card developed at NCAR.

  Table1. McGill X-band Vertically Pointing Radar

  Parameter	Value
  Wavelength/Frequency	3.2 cm (9410 MHz ± 30 MHz)
  Peak power	25 kW
  Dish diameter	1.2 m
  Pulse length	250 ns
  Pulse repetition frequency	1300 Hz
  Pulses averaged	1200
  Minimum height	100 m
  Maximum height	8000 m
  Bin size	15 m

  
  
  
• 2-D Video Disdrometer

  IIHR's video disdrometer is one of only a handfull of such instruments worldwide. It was specially manufactured for IIHR by Johanneum Research at The Institute for Applied Systems Technology, Inffeldgrasse, Austria. Two light sources generate orthogonal light sheets that are projected through narrow slits onto two line scan cameras. The optics are designed so that, seen through the camera lens, the slits appear evenly and brightly lit. Particles falling through the beams of light appear as dark silhouettes against this background. The light sources and cameras form the sensor unit that is exposed to the precipitation.

  The electronics and embedded computer that control the cameras and record the slit images are housed in a separate, weatherproof outdoor electronics unit. A second, indoor, PC communicates with this embedded computer via TCP/IP protocols. After copying the raw image information from the outdoor unit, the software running on the indoor PC reconstructs the shapes of the hydrometeros. The software also estimates the falling velocity, horizontal velocity, oblateness, and equivalent water content, for each individual hydrometeor. In addition to this information, aggregate information such as drop size distribution, rainrate versus time, vertical velocity versus time, oblateness versus diameter, etc. are computed and displayed in real-time. IIHR's disdrometer has been in operation since the middle of summer 1997, and we have collected data and written software to facilitate off-line analysis.

• Mobile Platform

  The instruments described above (i.e. vertically pointing radar, raingauges, and 2-D video disdrometer) are carried around on a 16 ft. trailer, called IIHR Mobile Rainfall Observatory. The trailer permanently houses the vertically pointing radar and accommodates the on-site data collection by the 2-D video disdrometer. For the raingauges, it merely serves as a hauling platform, but it houses the data acquisition and power distribution system too. We do not recommend, due to safety reasons, operating the radar while the trailer is in motion.

  The trailer is outfitted with a dual voltage electric wiring (12V DC and 120V AC). This way an external power supply can be provided by a cable from a permanent facility, or from a diesel powered generator or a set of batteries. On-site computer data acquisition system allows long term operation and storage of large volume of data. The radar antenna is covered with a fiberglass dome, which mitigates the effect of attenuation by the layer of water collected on the cover during rainfall.

• Rain gauge networks

  There will be approximately 30 rain gauges deployed in two separate clusters. Approximately 10 rain gauges will be installed at existing field mill sites within Kennedy Space Center (KSC). These rain gauges will enhance the existing network at KSC. Because the average gauge spacing is ~5km, the information provided by the KSC rain gauge network will help determine the mesoscale variabilith of rainfall across Cape Canaveral and provide ground truth for scanning radar. Indeed, the KSC rain gauge network is currently used to calibrate radar reflectivity (Z) - rainfall (R) estimates of rainfall for TRMM from the Melbourne NEXRAD.

  The spacing of the KSC gauges is too course to provide detailed statistics of rainfall at the convective scale in TEFLUN-B. Also, it was recognized that there exists a signigicant amount of restricted airspace in the vicinity of KSC, thus hampering the ability of aircraft to sample convection in this area. Because an important component of TRMM TEFLUN B is to provide combined aircraft and ground-based sampling of Florida convection, an additional site was selected for the placement of a dense rain gauge network (DRGN). A tentative site for the DRGN was chosen near the town of Hollopaw, Fl. These gauges will be used to examine variability of raingall at 0.5-2.0 km scales and should provide information on the range-dependency of scanning radar Z-R estimates of rainfall (as well as Z_DR-R, K_DP-R and other polarimetric relations). Moreover, profiler-pair will be able to provide vertical structure information on the precipitation characteristics (including drop size distributions) that can serve as calibration for the scanning radars. The combination of the DRGN, profiler and scanning radars will provide a unique picture of the vertical and horizontal variability during the TEFLUN B campaign.

• Rain Gauges & Disdrometers

  The rain gauges are tipping bucket type (Qualimetric). A number of disdrometers will also be deployed as part of the TEFLUN B ground validation program. Three types of disdrometers will be used: 2-D video, Joss, and APL. The 2-D and Joss will be deployed at the profiler site in conjunction with an APL and a tipping bucket rain gauge. The purpose of having all 3 disdrometer types at the profiler types will be to not only compare the surface based measurements of drop size distribution characteristics with the vertical structure (profiler), but also to compare the surface measurements collected by each disdrometer to address the strengths and weaknesses of each unit (address low end sensitivity of the APL disrometer).

  Approximately 5-10 additional APL disdrometers will be used in TEFLUN B. These disdrometers represent a new technology in disdrometer design. They are capable of storing several weeks of data at a time and will be stand-alone units. However, it should be noted that these systems are relatively new (being only deployed in TEFLUN A) and their reliability is not known. Also, as it currently stands, the low-end sensitivity of the APL disdrometer is approximately 1 mm and may therefore bias the retrieved DSD characteristics.

TEFLUN-B UND Citation II Microphysics Aircraft

The UND Cessna Citation II aircraft has a number of design and performance characteristics which make it a versatile and comparatively low cost platform for a wide range of atmospheric studies. The Citation II is a twin engine fanjet with an operating ceiling of 43,000 feet (12.1 km). The turbofan engines provide sufficient power to cruise at speeds of up to 340 knots (175 m/s) or climb at 3300 feet/min (16.8 m/s). The fanjet engines have relatively low fuel consumption at all altitudes, giving the Citation an on-station time of up to 4 hours or more, depending on mission type. Long wings allow it to be operated out of relatively short airstrips and to be flown at ths slower speeds (140 kts or 72 m/s) necessary for many types of measurements. The Citation is certified for flight into known icing conditions.

The cabin measures approximately five feet in diameter and more than 16 feet in length. The minimum flight crew is pilot, co-pilot and data system operator. Two additional seats are avbailable for scientific observers.

A series of structural modifications have been made to the basic airplane including the following:

1. pylons under the wing tips for a variety of probes in the undisturbed air flow away from the fuselage;
2. a heated Radome with a five hole system for wind measurement;
3. side-facing camera mounts for time lapse cameras;
4. optically flat glass windows for photography;
5. and an air inlet port for air sampling inside the pressurized cabin.

More details about the UND Citation can be found at the University of North Dakota aerospace research site.

Instrumentation:

The basic instrumentation package measures temperature, dew point temperature, pressure, wind and cloud microphysical characteristics along with aircraft position, attitude and performance parameters. The three dimensional wind field is derived from measurements of acceleration, pitch, roll and yaw combined with angles of attack and sideslip and indicated airspeed. An LTN-76 inertial navigation system and a global positioning system (GPS) supply the aircraft parameters. Turbulence intensity can be derived from differential pressure transducers and accelerometer outputs. Cloud microphysical measurements are made with an array of Particle Measuring Systems probes (FSSP, 1D-C, 2D-C, 1D-P) mounted on the wing tip pylons. These probes measure concentrations and sizes of particles from one µ to several millimeters in diameter. In addition, there are probes to measure both liquid water content (CSIRO) and icing rate (Rosemount icing meter). For TRMM two new instruments will be available, a Cloud Particle Imager (CPI) and a High Volume Particle Sampler (HVPS), both from SPEC, Inc. These will provide improved resolution above that which is achieved from the PMS probes. The CPI will provide microscopic quality images of small ice particles. The HVPS will replace the 1D-C probe and it will provide improved sample volumn for detection and imaging of large particles. A PMS 2D-P probe may also be used for periods when the HVPS is not available.

A forward or side-looking video camera is also used to provide a vbisual record of flight conditions and for recording of cockpit conversation. A Bendix-King vertical profiling forward looking weather radar can be viewed in the conkpit and recorded on videotape.

Data Acquisition and Display:

The data collected by the Citaiton can be sampled at various rates from 1 to 25 Hz. The sampling is controlled by the on-board computer system, which also displays the data in real time in graphic and alphanumeric formats while recording them on magnetic tape. The data system is based on a projetc-customized windows system to allow flexibility in data acquisition and instrumentation in order to accommodate specific research demands. The data system and power distribution systems were upgraded during 1996, which produced a substantial improvement in flexibility. also, an improved version of the data system was leased and adapted to fit the instruments. This provided a significant gain in weight and power availability.

When in the field, the Citation is accompained by a mobile operations support trailer. This vehicle houses thchnical support facilities, including calibration equipment for on-site quality control, and a workstation/ minicomputer system. The meteorological data collected on a research flight can thus be processed and examined within 24 hours.

Data Availability & Summary:

TEFLUN Data Protocol

TEFLUN Data Category

TEFLUN Priority Days

Data Availability Schedule

Tables of Flight Logs & Measurements

Coincidences of Ground, Aircraft & Satellite Measurements

TEFLUN-B/CAMEX-3 Flight Scenarios

Data Access:

TEFLUN data resides on DISC anonymous FTP. You may access the files from this document,

TEFLUN Data

or directly via FTP at

ftp disc2.nascom.nasa.gov
login: anonymous
password: < your internet address >
cd data/TEFLUNB/

Page Author: Hydrology Data Support Team -- hydrology-disc@listserv.gsfc.nasa.gov Web Curator: -- Website Curator: Stephen W Berrick NASA official: Steve Kempler, DISC Manager -- kempler@disc.gsfc.nasa.gov