CAMEX-4 2nd Generation Precipitation Radar

Table of Contents

1. Introduction
2. Instrument Description
3. Data Format and Naming Conventions
4. Data Products
5. Contact Information

1. Introduction

The Convection And Moisture EXperiment (CAMEX) is a series of field research investigations sponsored by the Earth Science Enterprise of the National Aeronautics and Space Administration (NASA). The fourth field campaign in the CAMEX series (CAMEX-4) ran from 16 August to 25 September, 2001 and was based out of Jacksonville Naval Air Station, Florida. CAMEX-4 focused on the study of tropical cyclone (hurricane) development, tracking, intensification, and landfalling impacts using NASA-funded aircraft and surface remote sensing instrumentation.

The Second Generation Precipitation Radar (PR-2) is a dual-frequency, Doppler, dual-polarization radar system that includes digital, real-time pulse compression, extremely compact RF electronics, and a large deployable dual-frequency cylindrical parabolic antenna subsystem. The PR-2 radar flew on the NASA DC-8 aircraft during the field experiment.

The Jet Propulsion Laboratory PR-2 team has created a document titled 'User's Guide to CAMEX-4 PR-2 Data'. This document is included with this dataset, and is available in either PDF or MS Word format from this ftp site.

Chapters in the User's Guide are:

Due to the completeness of the User's Guide, this document will only highlight some of the information found therein.

2. Instrument Description

The airborne PR-2 system includes a real-time pulse compression processor, a fully-functional control and timing unit, and a very compact LO/IF module, all of which could be used in spaceborne applications. The cylindrical reflector antenna and linear feed array for the spaceborne PR-2 have been replaced by traveling wave tube amplifiers (TWTAs), front-end electronics, and an offset parabolic reflector antenna with mechanical scanning. The airborne PR-2 operational geometry is shown in Fig. 1; it looks downward and scans its beam across-track, with each scan beginning at 25 degrees to the left of nadir and ending at 25 degrees to the right. It uses the same scanning antenna reflector as that used for the Airborne Rain Mapping Radar (ARMAR) [3]; it consists of a 0.4 m offset reflector antenna with a mechanically scanned flat plate. For PR-2 the 13.8-GHz antenna feed has been replaced by a dual-frequency feed (13.4 and 35.6 GHz) and the aperture at 35.6 GHz is under-illuminated to provide matched beams at the two frequencies. This choice results in poor Doppler accuracy at Ka-band, but is needed for rain retrieval.

PR-2 Parameters are shown in the table below:

Frequency 13.4 GHz 35.6 GHz
Polarization HH/HV HH/HV
Antenna diameter 0.4 m 0.14 m
Beamwidth 3.8 deg 4.8 deg
Antenna gain 34 dBi 33 dBi
Antenna sidelobe -30 dB -30 dB
Polarization isolation -25 dB -25 dB
Peak power 200 W 100 W
Bandwidth 4 MHz 4 MHz
Pulse width 10-40 ms 10-40 ms
PRF 5 kHz 5 kHz
Vertical resolution 37 m 37 m
Horizontal resolution 800 m 800 m
Ground Swath 10 km 10 km
Noise-equiv. Ze
(10 km range)		 5 dBZ 5 dBZ
Doppler precision 0.4 m/s >1 m/s

3. Data Format and Naming Conventions

Data are 'tarred' into daily (mission) data files of the form:

c4dpr2_yyyy.ddd_010mmm.tar

where c4d announces that data is from CAMEX-4 and that the instrument flew aboard the NASA DC-8. pr2 indicates the instrument. yyyy.ddd is the four digit year and day of year, 010mmm is the mission number, and finally, .tar is the tar file extension.

When untarred, this file will yield a 'set' of files whose number depends on the length of the mission. Each 'set' will consist one data file and at least three image files from the Ku-band and possibly two additional images from the Ka-band antenna.

Raw data files are named as:

c4dpr2_yyyy.mmdd_010mmm_tttt.hdf

Naming convention is similar to that shown above. But, instead of yyyy.ddd, we have yyyy.mmdd (year, month, day) and an addition of a tttt group which represents the start time of the data scan. The file extension is also different, as these are .hdf files. More information about HDF may be found at the HDF homepage. This format is similar to that from the TRMM Precipitation Radar.

As with the instrument description, detailed information may be found in the User's Guide.

The three image files associated with each data file have names of the form:

c4dpr2_yyyy.mmdd_010mmm_tttt_(type).jpg

The name is very similar to the data file name, but contains the .jpg extension indicating an image file, and a (type) which is either Dop (Radial doppler velocity), KuLdr (Ku band linear depolarization ratio), KuZ (Ku band radar reflectivity) KaLdr (Ka band linear depolarization ratio) and KaZ (Ka band radar reflectivity).

4. Data Products

The data producers have provided code named read_pr-2_lev1b_hdf.pro for use in extracting data from the HDF files. This code is used with IDL, a commercial data processing package available from Research Systems, Inc.

The code is shown below, and is also included with the dataset. Additionally, it may be found here.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;                                                                         ;
;           program read_pr-2_lev1b_hdf.pro                               ;
;                                                                         ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; PURPOSE:     An IDL Procedure for reading a JPL PR-2 data file. 
; DATA FORMAT: Please refer to "User's guide to CAMEX-4 PR-2 data" for 
;              details.
;
;Copyright (C) 2002, California Institute of Technology. U.S. Government
;Sponsorship under NASA Contract NAS7-1270 is acknowledged.
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

pro read_pr-2_lev1b_hdf, filen, zhh_ku, ldr_ku, vel_ku, zhh_ka, $
look_vector, range0, isurf, sequence, vsurf, $
vsurfdc8, no_av, fileheader, scantime, alt_r, lat, lon


; Open the file for read and initialize the Vdata interface
file_handle = hdf_open(filen,/read)

; get the fileheader Vdata
vdata_ID = hdf_vd_find(file_handle,'fileheader')
vdata_H = hdf_vd_attach(file_handle,vdata_ID)
hdf_vd_get,vdata_H,name=name,fields=raw_field
nscan = hdf_vd_read(vdata_H, fileheader)
hdf_vd_detach, Vdata_H

; get the scantime vdata
vdata_ID = hdf_vd_find(file_handle,'scantime')
vdata_H = hdf_vd_attach(file_handle,vdata_ID)
nscan = hdf_vd_read(vdata_H, scantime)
hdf_vd_detach, Vdata_H

; get the alt_r vdata
vdata_ID = hdf_vd_find(file_handle,'alt_r')
vdata_H = hdf_vd_attach(file_handle,vdata_ID)
nscan = hdf_vd_read(vdata_H, alt_r)
hdf_vd_detach, Vdata_H

; Find the scantime vdata
vdata_ID = hdf_vd_find(file_handle,'lat')
vdata_H = hdf_vd_attach(file_handle,vdata_ID)
nscan = hdf_vd_read(vdata_H, lat)
hdf_vd_detach, Vdata_H

; Find the scantime vdata
vdata_ID = hdf_vd_find(file_handle,'lon')
vdata_H = hdf_vd_attach(file_handle,vdata_ID)
nscan = hdf_vd_read(vdata_H, lon)
hdf_vd_detach, Vdata_H

; Close the hdf file
hdf_close,file_handle


; Initialize the scientific data set interface (hdf_sd* routines)
sdsfileid = hdf_sd_start(filen,/read)

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'zhh14'))

hdf_sd_getdata, sds_id, zhh_ku

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'ldr14'))
hdf_sd_getdata, sds_id, ldr_ku

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'vel14'))
hdf_sd_getdata, sds_id, vel_ku

ka_begin= fileheader(16)
ka_end = fileheader(17)
if( (ka_begin ge 0) and (ka_end gt ka_begin) ) then begin
sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'zhh35'))
hdf_sd_getdata, sds_id, zhh_ka
endif

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'look_vector'))
hdf_sd_getdata, sds_id, look_vector

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'range0'))
hdf_sd_getdata, sds_id, range0

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'isurf'))
hdf_sd_getdata, sds_id, isurf

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'sequence'))
hdf_sd_getdata, sds_id, sequence

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'v_surf'))
hdf_sd_getdata, sds_id, vsurf

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'v_surfdc8'))
hdf_sd_getdata, sds_id, vsurfdc8

sds_id = hdf_sd_select(sdsfileid,hdf_sd_nametoindex(sdsfileid, 'no_av'))
hdf_sd_getdata, sds_id, no_av

hdf_sd_end, sdsfileid

return
end

Once again the user is directed to the User's Guide for additional information about the data format.

5. Contact Information

Data can be ordered and questions addressed at http://ghrc.nsstc.nasa.gov/.

To order this 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: ghrc@eos.nasa.gov

[NASA logo] NASA Information Contact: Michael Goodman, Global Hydrology and Climate Center
GHRC Web Curator: GHRC Web Team
Last update: Tuesday, 12-Jun-2007 16:55:43 CDT
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