NAMMA - NASA Polarimetric Doppler Weather Radar (NPOL)

Table of Contents

Introduction

This dataset consists of a collection of products derived from the NASA NPOL S-band radar observations that were collected during the NAMMA campaign, from 19 August through 30 September 2006, at Kawsara, Senegal. A total of 7200 scans were archived during the campaign, with over 29 GB of data collected. Additional in-depth information can be found here: NPOL_NAMMA_Product_Documentation.pdf

Instrument Description

The NASA Polarimetric Radar (NPOL), developed by a research team from Wallops Flight Facility, is a fully transportable and self-contained S-band research radar. It has an ultra-modern flat panel hexagonal antenna 18 feet (5.5 meters) in diameter. The radar requires no special site preparation and can be set up on a generally flat area anywhere in the world. The system can operate continuously, 24 hours a day, 7 days a week, measuring both rainfall rates and amounts.

Scanning Strategy

NPOL collected 360º PPI data (no sectors or RHIs) and operated nearly continuously during NAMMA. The radar operated on a 15-minute repeat cycle, starting at the top of the UTC hour. During each 15-minute period, a 1-tilt (0.8º) surveillance scan (270 km maximum range) and one 19 tilt volume scan (150 km maximum range) were collected. The multiple tilt volume was chosen according to the existing conditions.
There were 2 options:

NAMMA_FAR_S scanning strategy:
19 angles from 0.7 to 33.0 degrees: 0.7, 1.4, 1.8, 2.3, 3.4, 4.5, 5.7, 6.9, 8.2, 9.6, 11.3, 13.0, 15.0, 17.2, 19.8, 22.5, 26.5, 29.5, 33.0 (This scan was used most often during the field campaign)

NAMMA_NEAR_S scanning strategy:
19 angles from 0.8 to 49.0 degrees: 0.8, 1.5, 3.2, 5.5, 7.9, 10.3, 12.7, 15.1, 17.6, 20.0, 22.6, 25.1, 27.8, 30.5, 33.2, 36.1, 39.1, 44.0, 49.0 (This scan was used occasionally when storms were near NPOL)

Volume scan setup for both scan types:

Resolution: 1.4 degrees (azimuth)
Pulse Width: 0.80
Polarization: H + V
Samples: 128
Start Range: 0.00 km/Bin Spacing: 199.9 m
Max Range: 150.0 km
Unambiguous Range/Velocity: 157.8 km/25.4 m/s
High/Low PRF: 950 Hz

Collected Parameters

The following information is the same for both scanning strategies listed above. NPOL collected a variety of conventional and polarimetric fields during NAMMA. The following is a list of parameters and their definitions:

ZT: Total unfiltered reflectivity (dBZ)
DZ: Noise filtered reflectivity (dBZ)
VR: Mean Doppler velocity (m s-1)
SW: Spectral width (m s-1)
ZDR: Differential reflectivity (dB)
KDP: Specific differential phase (deg/km)
PhiDP: Differential phase (deg)
RhoHV: Correlation between horizontal and vertical polarizations (0 to 1)

Data Products

For the NAMMA field campaign, four different radar products are available from NPOL:

1.Quality control (QC) volume data
2. Quick look gif files of the base reflectivity PPI images
3. Six-level gridded Cartesian reflectivity maps at a 2 km horizontal resolution
4.One-level gridded Cartesian rainfall rate map at a 2 km horizontal resolution

QC volume data:

Radar data files (Universal Format (UF)) of unfiltered radar reflectivity “ZT”, uncorrected radar reflectivity “DZ”, corrected radar reflectivity “CZ”, radial velocity “VR”, spectral width “SW”, differential reflectivity “DR”, correlation “RH”, differential phase “PH”, and specific differential phase “KD”. The files have been organized by type (volume scan or surveillance), and have been subsetted into directories by day (060831/ : 31 August 2006). The filenames have the following format: NAMMA_NPOL_QC_YYMMDD_HHMM.uf.gz: (Example: NAMMA_NPOL_QC_060831_0900.uf.gz: NPOL QC’ed file for 31 August 2006 at 0900 UTC. The file is in UF format and has been gzipped). The “CZ” field was used to create the gridded reflectivity and rainfall map files described below.

Quick look reflectivity images:

Individual image files (gif format) of uncorrected radar reflectivity created by the radar data acquisition and display software (IRIS: Interactive Radar Information System) used with NPOL are available for all the surveillance scans collected during NAMMA. The images provide a “snapshot” of storm activity out to a maximum range of 270 km from NPOL.

Gridded reflectivity files:

Radar-reflectivity maps at a 2.0 km horizontal resolution and 2.0, 4.0, 6.0, 8.0, 10, and 12.0 km vertical levels were created and mapped to a 556 x 556 common grid that corresponds to a 10° x 10° latitude-longitude area centered on NPOL during NAMMA. The grid domain is larger than the maximum range of NPOL. However, this same grid has been developed to ingest TRMM PR for that region for longer-term climatological analysis. The Cartesian maps were created using software developed by the PI. The gridded files are stored in netCDF format. The reflectivity values are stored in units of dBZ. There are two flags in the files:

-88.0: A grid outside the maximum range of NPOL
-99.0: Inside the maximum range of NPOL, but no echo was detected

Gridded rainfall rate files:

The gridded rainfall rate files have a similar format as the reflectivity files. They are mapped to the same common domain. The rainfall rates are mapped to one level at a height of 2 km. The units are in mm h-1. There is one flag: -88.0, which corresponds to a grid outside the maximum range of NPOL. A value of 0.0 mm h-l indicates no echo was detected by NPOL.

File Naming Convention and Format

Image files:

NAMMA_NPOL_yymmdd_tttt_dz.gif  (gif format)

These are individual image files (gif format) of uncorrected radar reflectivity “dz”, where "yymmdd" is year, month, day and "tttt" is time.

Gridded data files (rainfall and reflectivity):

NAMMA_NPOL_yymmdd_tttt_cart_2.0kmdz.dat.gz
NAMMA_NPOL_yymmdd_tttt_cart_2.0kmrr.dat.gz

These are gridded reflectivity files, "dz", and gridded rainrate files "rr", both  in NETCDF format, where "yymmdd" is year, month, day and "tttt" is time. The files are compressed via gzip.

Radar data files (surveillance and volume scan):

NAMMA_NPOL_SUR_QC_yymmdd_tttt_uf.gz
NAMMA_NPOL_VOL_QC_yymmdd_tttt_uf.gz

These are radar data files (Universal format) of unfiltered radar reflectivity “ZT”, uncorrected radar reflectivity “DZ”, corrected radar reflectivity “CZ”, radial velocity “VR”, spectral width “SW”, differential reflectivity “DR”, correlation “RH”, differential phase “PH”, and specific differential phase “KD”, where "yymmdd" is year, month, day and "tttt" is time. These are the data files used (CZ fields) to generate the gridded NETCDFs described above.

Example Software

Contact the PI if you would like to work with the data in UF format or use sample software written using RSL. The PI can provide example software to read and manipulate the UF files.
An example program (netcdf2ascii.c) to read the netCDF product files, along with a sample makefile, has been included with this data release. The general purpose of this program is to convert the netcdf files created for this project into a readable ASCII format. The web link in the "Introduction" section of this document provides information on how to use the provided software.

Contact Information

The data producer is:

Paul A. Kucera (P.I.)
E-mail: pkucera@ucar.edu

To order these data or for further information, please contact:

Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/