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ER-2 Doppler Radar (EDOP) Data from TRMM LBA


EDOP image, flight of 1/25/99
EDOP image from ER-2 flight of January 25, 1999

Introduction
Sponsor
Data Description
Data Format
Read Software
EDOP Calibration
Specific Issues for Field Campaigns
References
Data Access and Contacts
Read Software
FTP Site
Points of Contact

Hourly Images Flight leg Images EDOP V2.1 data in Universal Format

Introduction

The ER-2 Doppler radar (EDOP) is an X-band (9.6 GHz) Doppler radar mounted in the nose of ER-2. The instrument has two fixed antennas, one pointing at nadir and the second pointing approximately 33 degree ahead of nadir. The beam width of the antenna is 3 degree in the vertical and horizontal directions which, for a 20 km altitude, yields a nadir footprint a the surface of 1 km. The ER-2 ground speed is nominally 210 m/s and the integration period used by the data system is 0.5 second. The transmit pulse is 0.5 second and the gate spacing is over sampled at 37.5 meter interval. Minimum detectable reflectivity is about -10 dBZ at an altitude of 15 km and for a 0.375 meters range gate spacing. Additional details of the radar and processing are described by Heymsfield et al. (1996).

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 Dr. Gerald Heymsfield of the Laboratory for Atmospheres, Mesoscale Atmospheric Processes Branch, NASA Goddard Space Flight Center, and Nelson Ferreira, Instituto Nacional de Pesquisas Espaciais, Brasil, for the production of these data and the Data and Information Services Center(Code 610.2) at the Goddard Space Flight Center, Greenbelt, MD, which archives and distributes them under sponsorship of NASA's Earth Science Enterprise.

Data Description

EDOP Data Format

EDOP data is in Universal Format (UF) as documented in the UF-IDL.guide in the directory uf_software described in the last section of this document. 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.

The current distribution (version 2) is in Level 3 format, and will have a "uf.2.1" appended to the file name. The ".2" 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
  • PF Forward_VV power
  • PX Forward_VH power

  • DN Nadir_VV raw Doppler velocity [m/s]
  • DS Nadir_VV raw surf Doppler velocity [m/s]
  • DF Forward_VV raw Doppler velocity [m/s]
  • DX Forward_VH raw doppler velocity [m/s]

  • WN Nadir_VV spectral width [m/s]
  • WS Nadir_VV surface spectral width [m/s]
  • WF Forward_VV spectral width [m/s]
  • WX Forward_VH spectral width [m/s]

  • MN Nadir_VV power (dBM)
  • MS Nadir_VV surface power (dBM)
  • MF Forward_VV power (dBM)
  • MX Forward_VH power (dBM)

  • ZN Nadir_VV reflectivity (dBZ)
  • ZS Nadir_VV reflectivity (dBZ)
  • ZF Forward_VV reflectivity (dBZ)
  • ZX Forward_VH reflectivity (dBZ)

  • VN Nadir_VV corrected doppler velociy (m/s)
  • VF Forward VV corrected doppler velocity(m/s)

Read Software

IDL software for reading the data is available at the DISC.

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.

SPECIFIC ISSUES FOR FIELD CAMPAIGNS

TEFLUN-A

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. A 1.85 dB adjustment (decrease) was incorporated in the current distribution of the nadir reflectivity, based on all avaliable 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. Again, the best estimate calibration data has been implemented on 4 May data. The forward cross polarzation is not available for this day.

CALIBRATION CORRECTION AND 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.
VERSION 2.0 - Released February, 2000
Changes from Version 1.0:
  1. Problems 1 and 2 above have been corrected: - Calibration has been adjusted by 2.51 dB on all channels. - Latitude - longitude values have been corrected.

TEFLUN-B/ CAMEX-3

See 1 and 2 above.

TRMM-LBA

See 1 and 2 above. Otherwise very clean data sets.

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.

Data Access and Contacts

All EDOP products are available on DISC anonymous ftp.

FTP Site

ftp disc2.nascom.nasa.gov
logon: anonymous
passwd:
cd data/trmm-lba/aircraft/er-2/edop

Points of Contact

The Principal Investigator for the EDOP data is

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

heymsfield@agnes.gsfc.nasa.gov

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

tian@agnes.gsfc.nasa.gov

For additional information, please contact the GES DISC User Services:

GES DISC User Services
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
301-614-5224
Email: help-disc@listserv.gsfc.nasa.gov
Last update:Wed Dec 24 08:25:34 EST 2003
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