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SCSMEX Radar Data

Introduction
The Campaign
Sponsor

The Data
QC Corrections

The Files
Format
Naming Convention

Data Access & Contacts
Order Data
Points of Contact

Order SCSMEX Radar Data from the DISC

Introduction

The Campaign

The South China Sea Monsoon Experiment took place between the period of 1 May - 30 June 1998. There was a network of two ground-based radars, which was among the many instruments that were deployed during the experiment. The radar network was located in the center of the experimental area and was positioned about 300 km SE of Hong Kong in the South China Sea. Both radars were 5cm wavelength and had Doppler capability. The BMRC CPOL had the additional capability of being polarimetric. TOGA was located about 40 km SSE of CPOL.

Radar data collection started on 4 May 1998 and ended on 25 June 1998. This document describes the quality controlled (QC) TOGA and CPOL radar datasets. The remaining sections of the document will describe the file naming convention and organization, a brief description of the QC corrections, and contact information.

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 Jian-Jian Wang of the Mesoscale Atmospheric Processes Branch (Code 912), Goddard Space Flight Center, Greenbelt, Maryland and Thomas Keenan, BMRC, Melbourne, Victoria, Australia for the production of these data and the Data and Information Services Center(Code 610.2) at the Goddard Space Flight Center, which archives and distributes them under sponsorship of NASA's Earth Science Enterprise.

The Data

QC Corrections

This section only briefly highlights the corrections. A more detailed analysis of the corrections (especially for TOGA) will be published in a separate manuscript, but these are the main corrections the user should be aware of.

A. TOGA Radar

TOGA had several problems that were discovered during and after the experiment and during post_experiment analysis. A major problem occurred in the second half of the experiment (intensive operation phase 2 (IOP2)). Water leaked into the cables that drive the antenna causing problems in knowing the exact location of the antenna. The geolocation of the data recorded during IOP2 (4 June - 25 June, 1998 FOR TOGA) are not known with any certainty and are therefore excluded from the QC dataset.

  1. Doppler Velocity

    • Incorrect sign convention
      The Doppler velocity stored in the raw data had the incorrect sign (+/-). By convention, Doppler radial velocities towards the radar are negative values and away are positive. They were opposite in the raw data.

    • Ship motion correction
      Normally, ship motion is subtracted out of the Doppler velocity by feeding in the ship motion obtained by an independent inertial navigation unit (INU). This setting was not turned on in the radar processing software. Fortunately, ship motion is stored in every ray of data and has been subtracted from the data. The ship motion was not large during IOP1. The maximum value seen in QC tests was about 0.4 m/s.

  2. Radar Reflectivity

    • Known engineering offset After the experiment, engineering tests of the radar discovered a mismatch in the bandpass filter. This mismatch caused the TOGA radar to have a 5.5dB decrease in the returned power. Therefore, a +5.5dB offset needed to be added to the reflectivity data for this correction.
    • Unknown source offset Extensive comparisons with CPOL, raingauge, and disdrometer data revealed that TOGA reflectivity was still too low. It is +8.0dB based on these comparisons. The source of this offset is still under investigation.

CORRECTIONS TO RAW TOGA DATA
ParameterErrorCorrection
Doppler velocitySigns reversed(+/-)Signs reset to standard
Ship motion not accounted for in raw doppler velocitiesCorrected using information stored in ray of data
Radar reflectivityKnown engineering offset: bandpass filter mismatch caused 5.5dB deficit in returned powerApplied +5.5dB to each reflectivity value
Unknown source offset: CPOL and gauge comparisons indicate remaining 8.0dB reflectivity deficitApplied +8.0dB to each reflectivity value

B. CPOL Radar

CPOL had very few documented problems during SCSMEX. It operated almost continuously from 4 May 1998 to 25 June 1998. The only major problem occurred with the elevation servo on the antenna. It was not operating between 27 May 1998 and 8 June 1998. During this time, CPOL could only operate in surveillance mode (lowest scan only.) The following is a brief description of the corrections, which was provided by Tom Keenan.

  1. Doppler Velocity

    The sign was flipped just like TOGA. This problem was discovered and corrected in the software on May 17. The correction had been applied to the data before this time. Also, it was discovered that Transmit/Receive (T/R) switch failed on 16 May. This affected the data out to 10 KM. After 16 May, the problem was corrected.

  2. Radar Reflectivity

    No corrections made.

  3. Polarimetric Variables

    The only correction that was applied to the QC dataset was for the T/R problem discovered on 16 May. It also affected the ADR field out to a range of 10 KM.

CORRECTIONS TO RAW CPOL DATA
ParameterErrorCorrection
Doppler velocitySigns reversed(+/-)Signs reset to standard
Radar reflectivityNo corrections
Polarimetric valuesTransmit/receive switch failure affecting data out to 10km before May 16

The Files

Format

The QC radar dataset have been converted to the standard radar universal format (UF) and compressed using the standard UNIX gzip utility.

Naming Convention

For both radars, data is stored in daily directories. For example, the directory 980515/ contains all the data for 15 May 1998.

A. TOGA radar

  1. Volume scans

    Volume scan data have the following naming convention:

    SITE_scantype_YYMMDD_HHMN.uf.gz
    where:

    SITE: TOGA for TOGA radar
    scantype: vol for volume scan
    YY: Year
    DD: Day
    HH: Hour (UTC)
    MN: Minute (start of the scan)
    uf: Universal Format file
    gz: gzipped

    For example, TOGA_vol_980515_0400.uf.gz

    is a TOGA volume scan that was recorded on 15 May 1998 at 04:00 UTC and is stored as a compressed UF file.

  2. Surveillance Scans

    Surveillance scan data have the same naming convention as volume scans except the scantype identifier is sur instead of vol

    where

    YY = year (1999)
    MM = month
    DD = day of month
    HH = UTC hour
    mm = minutes after the hour

B. CPOL radar

  1. Volume and Surveillance Scans
  2. Both volume and surveillance scans have the same naming convention. The QC UF files from the CPOL radar were generated by a QC program provided by Dr. Tom Keenan. This program was applied to the raw CPOL files and no attempt was made to modify the code or outpur naming convention. The filenames have the following format: ufYYMMDD_HHMMSS.PPI.gz
    where: uf = Universal Format file
    YY = year (1999)
    MM = month
    DD = day of month
    HH = UTC hour
    MN = minutes (start of scan)
    SS = Second (start of scan)
    PPI = PPI (Plan Position Indicator file (i.e. volume or surveillance as opposed to RHI (Range Height Indicator) file)
    gz = gzipped


Data Access and Points of Contact

Order Data

The TOGA and CPOL radar data may be ordered by email from the Hydrology Data Support Team, NASA Goddard (see below).

Points of Contact

The Principal Investigator for the SCSMEX radar data is

Jian-Jian Wang
Mesoscale Processes, Code 912
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
jwang@radar.gsfc.nasa.gov

Co-Investigator for the CPOL radar data is

Tom Keenan
Bureau of Meteorology (BMRC)
PO Box 1289k,
Melbourne, Victoria 3001
Australia
T.Keenan@BoM.GOV.AU
Fax : +61-(0)3-9669-4660

For technical questions on the radar data contact:

Paul Kucera
The University of Iowa
Iowa City, IA 52242
pakucera@mail.iihr.uiowa.edu

For SCSMEX user services at the DISC contact

Hydrology Data Support Team (Goddard DISC), Code 610.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
hydrology-disc@listserv.gsfc.nasa.gov (301) 614-5165 (voice)
(301) 614-5268 (fax)

Last update:Thu Aug 15 13:56:43 EDT 2002
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
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