Readme Contents

Data Set Overview

Sponsor

The Data

Characteristics

The Files

Format

Naming Convention

Companion Software

Data Access & Contacts

FTP Site

Points of Contact

The Science

Data Set Overview

The ER-2 Doppler (EDOP) Radar data sets of Texas & Florida Underflights field experiments (TEFLUN A & B) are part of the aircraft based measurements collected in support of the TRMM ground validation efforts.

EDOP instrument was flown on the NASA ER-2 aircraft over Texas from April 9 through May 6, 1998 for the TEFLUN-A experiment and over Florida from August5 through September 27, 1998 for the TEFLUN-B & CAMEX-3 field campaigns. Prior to this, the EDOP instrument collected the first reflectivity measurements during CAMEX-1(September 1993) and first Doppler measurements during January 1995 flights and CAMEX-2 (August 1995).

EDOP is an X-band (9.6 GHz) Doppler radar nose-mounted in the ER-2. The instrument has two antennas: one nadir-pointing with pitch stabilization, and the other forward pointing. The general objectives of EDOP are the measurement of the vertical structure of precipitation and air motions in mesoscale precipitation systems and the development of spaceborne radar algorithms for precipitation estimation such as will be used for the Tropical Rain Measuring Mission (TRMM).

The EDOP measurements were made under the direction of the NASA/GSFC scientists Dr. Gerald Heymsfield(Principal Investigator). The EDOP data sets for all TRMM field campaigns are archived here at the Goddard Data and Information Services Center (DISC).

Sponsor

The distribution of these data sets is funded by NASA's Earth Science Enterprise. The data are not copyrighted; however, we request that when you publish data or results using these data, please acknowledge as follows:

The authors wish to thank NASA/GSFC scientist Dr. Gerald Heymsfield for the production of this EDOP data set. They also thank the Data and Information Services Center (Code 610.2) at the Goddard Space Flight Center, Greenbelt, MD, 20771, for making it available to the scientific community. Goddard's contribution to the distribution and archive of this data set was sponsored by NASA's Earth Science Enterprise.

The Data

Characteristics

The data is very preliminary, before using this data in your publication, please contact the Principal Investigator Dr. Gerald Heymsfield ( heymsfield@agnes.gsfc.nasa.gov).

The Files

EDOP Data Format

EDOP data is in Universal Format (UF) as documented in the UF-IDL.guide in the directory uf_software. EDOP currently collects data at a rate of 2 Hz from 4 Doppler channels with 738 gates. Nadir rain (dynamic range optimized for rain signal -10-70 dBZ) Nadir surface (dynamic range optimized for surface 20-100 dBZ) Forward Co-polarization Forward Cross-polarization Each of these channels provides reflectivity, Doppler velocity, and spectral width estimated from the time series (autocovariance) approach.

Four levels of UF format are implemented for EDOP data:

Level 1: Conversion of EDOP uncalibated raw data format to UF (uncalibrated power, Doppler velocity).

Level 2: Conversion of uncalibrated power to calibrated dBZ

Level 3: Doppler unfolding and aircraft motion removal.

Level 4: Attenuation correction of reflectivity.

File Naming Convention

The current distribution (Version 1) is in Level 2 format, and will have a ".uf.1" or ".caluf.1" appended to the file name. The ".1" is the version number and updated data sets will have higher numbers. All data files without a number appended are Version 0 and should be replaced with higher versions of the data.

The parameter names for the Level 2 files are as follows:

   PN  Nadir_VV power
   PS  Nadir_VV surface power

   DN  Nadir_VV raw Doppler velocity [m/s]
   DS  Nadir_VV raw surface Doppler velocity [m/s]

   ZN  Nadir_VV reflectivity (dBZ) 
   ZS  Nadir_VV surface reflectivity (dBZ)

 

Companion Software

The EDOP dataset was generated using PC computer, in order to read the data on UNIX, an IDL software is provided here for the convenience.

Data Access and Contacts

Data Access

FTP Site

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

EDOP Calibrated Data(Binary files)

EDOP Browse Images

or directly via FTP at

ftp disc2.nascom.nasa.gov

login: anonymous

password: < your internet address >

cd data/TEFLUNA/aircraft/nasa_er2/edop

Points of Contact

For Information about TEFLUN data at Goddard DISC, please contact

Hydrology Data Support Team
Goddard DISC, Code 610.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771 Email: hydrology-disc@listserv.gsfc.nasa.gov

Technical Inquiries about this Data should be addressed to EDOP Data Investigators::

Gerald Heymsfield
Laboratory for Atmospheres, Mesoscale Atmospheric Processes Branch
Goddard Space Flight Center
Code 912
Greenbelt, MD 20771
301-614-6369 (voice)
(301) 614-5558 (fax)

Internet: heymsfield@agnes.gsfc.nasa.gov

Lin Tian
University Space Research Associates &
Goddard Space Flight Center
Code 912
Greenbelt, MD 20771
301-614-6369 (voice)
(301) 614-5558 (fax)

Internet: tian@agnes.gsfc.nasa.gov

The Science

The EDOP radar is an X-band (9.6 GHz)radar with two fixed antennas, one pointing at nadir and the second pointing approximately 33.5 deg forward of nadir. A transmit pulse with vertical linear polarization is sent to both antennas. Reflectivity and Doppler information are received from both the nadir and forward antennas.

EDOP measurement's goals for TRMM field campaigns include:

• Vertical structure of the reflectivity and vertical velocity in the hurricane precipitation region, especially the inner core region and the upper level divergent outflow.
• Evaluation of TRMM radar algorithms for attenuation and rain rates.
• The relation of radar-derived vertical circulations to temperature and moisture structure deduced from radiometric measurements.
• Identification and vertical structure of embedded cylones.
• Deducing microphysical information in hurricanes based on EDOP and microwave radiometer observations.

Algorithm

EDOP measures high-resolution time-height sections of reflectivity and vertical hydrometeor velocity (and vertical air motion when the hydrometeor fall speed and aircraft motions are removed). An additional capability on the forward beam permits measurement of the linear depolarization ratio (LDR) which provides useful information on orientation of the hydrometeors (i.e., the canting angle), hydrometeor phase, size, etc. The dual beam geometry has advantages over a single beam. For example, along-track horizontal air motions can be calculated by using the displacement of the ER-2 to provide dual Doppler velocities (i.e., forward and nadir beams) at a particular altitude.

EDOP is designed as a turn-key system with real-time processing on-board the aircraft. The RF system consists of a coherent frequency synthesizer which generates the transmitted and local oscillator frequencies used in the system, a pulse modulated (0.5 to 2.0 micro-second pulse) high gain 20 kW Traveling Wave Tube Amplifier which is coupled through the duplexer to the antenna, and the receiver which is comprised of a low-noise (~1dB) GaAs preamplifier followed by a mixer for each of the receive channels. The composite system generates a nadir oriented beam with a co-polarized receiver and a 350 forward directed beam with co- and cross- polarized receivers. The antenna design consists of two separate offset-fed parabolic antennas, with high polarization isolation feed horns, mounted in the nose radome of the ER-2. The antennas are 0.76 m diameter resulting in a 30 beamwidth and a spot size of about 1.2 km at the surface (assuming a 20 km aircraft altitude). The two beams operate simultaneously from a single transmitter.

EDOP uses a real-time processor to accommodate the very high data and processing rates required by the system's 4400 Hz pulse repetition frequency. The system obtains high vertical resolution profiles (37.5 meter spacing) of measured quantities. The EDOP system is designed to have both high sensitivity for detection of weaker precipitation returns and a large dynamic range since variations in one vertical profile can exceed 90 dB (including return from the surface). Minimum detectable reflectivity for the system is about -5 dBZ at an altitude of 15 km. In 1997 a new data system was implemented that serves both as a digital IF receiver and a data processing system. This new linear receiver has a wider dynamic range for Doppler measurements as compared with the previous system.

The sensor details can be obtained from the EDOP Home Page : http://rsd.gsfc.nasa.gov/912/edop/system_specs.htm.

EDOP Calibration

The calibration of EDOP is described in Caylor et al. (1995) although this has been modified somewhat due to the change to the new digital-IF receiver and processing system in 1998. After the calibration is obtained, EDOP surface measurements (sigma_0) from both the nadir and forward beams are compared with previously published values as well as with statistics from TRMM estimated values.

In addition, the reflectivity measurements in rain are compared with simultaneous measurements from the TRMM Precipitation Radar and several ground-based radars. However, only the EDOP internal and external calibrations are used and NO adjustments are made to the EDOP reflectivites (unless noted below) based on these comparisons. EDOP has a linear receiver so all calculations are performed linearly. Thus if any error in calibration exists, the bias will be constant over the full dynamic range of the measurements. The final calibration of EDOP should be accurate to approximately 1 dBZ.

Major Calibration Isuues

During TEFLUN-A, the EDOP nadir front end amplifier degraded just after the pre-campaign external calibration and before the first data flights. The low-noise amplifier gain was reduced by about 10 dB for most of the experiment. The nadir channel was corrected based on the above calibration procedures and then the forward and nadir channels were compared in rainy regions to determine if any biases existed. 1.85 dB adjustment (decrease) was made for the nadir channel based on all available knowledge. For the flight on 4 May, one digital receiver and processor boards were having problems. As a result, the nadir surface measurement uses a different board which required additional external calibrations after the field campaign. The forward cross polarzation is not available.

Calibration Correction & Other Known Problems (10/5/99):

1) A reflectivity calibration adjustment of -2.51 dB is required for all the Version 1 data sets. This adjustment is required because of the oversampling in range performed by EDOP. EDOP uses a digital bandpass filter and the filter in digital signal processing code was not being normalized by the pulsewidth. This resulted in a 3 dB calibration difference but filter losses were reduced (typically 1.8 dB) resulting in a net decrease in the calibration given above. This correction NOT included in Version 1 data.

2) The latitude and longitude values given in the UF files are incorrect in Version 1 data sets due to an incorrect scale factor used on the high-speed ARINC 429 navigation data. The scale factor used in Version 1 was 0.00017172 (S0), so it should have been 0.0001716614588 (SN). This results in an error to the west of about 0.02 degrees (~2 km) at 60deg West longitude (Rondonia Brazil), for instance. That is, Lon = (SN/S0) * Lon in current UF file. But it may be more accurate to use the navigation recorder data (in DISC) until the data gets reprocessed.

References

Caylor I.J., G.M. Heymsfield, S. Bidwell, and S. Ameen, 1994: NASA-ER-2 Doppler radar reflectivity calibration for the CAMEX project. NASA Tech Memo 104611, 15 pp.

Heymsfield, G. M., S. Bidwell, I. J. Caylor, S. Ameen, S. Nicholson, W. Boncyk, L. Miller, D. Vandemark, P. E. Racette, and L. R. Dod, 1996: The EDOP radar system on the high-altitude NASA ER-2 aircraft. J. Atmos. Oceanic Tech., 13, 795-809.

EDOP URL: http://rsd.gsfc.nasa.gov/912/edop/system_specs.htm