Summary of EPIC-2001 Rain Map Files

EPIC Rainmap files were generated using all surveillance scans  (3 tilt, 
full PPI) collected by the Ronald H. Brown (RHB) C-band radar while the 
ship was on-station in the ITCZ (12 September 2001 13Z - 1 October 2001 
07 UTC) at its nominal location of 10 N, 95 W.  For each date and 
time, 3 files are included:

1.  epic_rr_yymmdd_hhmm.gif
2.  epic_rr_yymmdd_hhmm.ps.gz
3.  epic_rr_yymmdd_hhmm.txt.gz

where yymmdd is the file date (e.g., 010912 is 12 Spetember 2001) and hhmm  
is the start of the surveillance radar scan in UTC.  The gif file (1) shows 
a 1-km height map (CAPPI) of rainfall intensity (mm hr-1).  The subtitle in 
these plots indicates the rain area and average rain rate for all grid 
points containing a rain rate equal to or exceeding 0.5 mm hr-1.  The .ps 
file (2) is a gzipped postscript version of the gif plot with better image 
quality.  The ascii txt file (3) is a gzipped file which contains header 
information about the rain map cartesian grid and data values of radar 
reflectivity (dBZ) and rain rate (mm hr-1) for each point in the grid domain 
at a height of 1 km.  The files listed above are located in the gif, ps, and 
ascii subdirectories which are further subdivided by date.

Radar Data QC

All of the radar reflectivity data used to generate rain maps have first been 
filtered to remove 2nd trip echo, sea clutter, and other spurious echos using 
software developed by the NASA TRMM Office.  No calibration correction has 
been applied to the RHB radar reflectivity data.  Also, no attempt has been 
made to correct for attenuation.

Gridding Procedure

The radar data were first interpolated from polar to cartesian coordinates 
using the NCAR REORDER software.  The grid size for each file extends 120 km 
in each direction from the nominal RHB location (10 N,95 W), which is 
at the center of the cartesian grid (x = 0, y = 0).

Note that the RHB radar was not stationary during the EPIC field program.
Because of the increasing radar beam height at far range and the 
non-stationary location of the ship around the interpolated grid origin 
(10 N, 95 W), there are occasional data losses in the 1 km height maps at 
far range (> 100 km).  It is therefore recommended that quantitative data 
analyses be restricted to 100 km of the grid origin.

Estimation of Rainfall Rates

Instantaneous rainfall maps were generated using the Reflectivty-Rainfall (Z-R) 
relationship: Z=218*R(1.6).  This relationship was derived from analysis of 
2D-P data collected on-board the NCAR C-130 aircraft during the ITCZ portion of 
EPIC-2001.

Reading the Ascii Data File

The data values are written from the lower left hand portion of the grid 
(-120,-120) with all values in the X-direction  (east-west) written for a given 
y value (north-south).  Thus, the first line of the reflectivity and rain data 
consists of 241 data points: (-120,-120), (-119,-120), (-118,-120)...(120,-120).  
The 2nd line consists of the next 241 data points: (-120,-119), (-119,-119), 
(-118,-119)...(120,-119).  The last line consists of the the last 241 points: 
(-120,120), (-119,120), (-118,120)...(120,120).

Note:  A more complete readme file including figures is provided with the data

Questions concerning the EPIC rain map products can be directed to:
Rob Cifelli (rob@atmos.colostate.edu) or
Walt Petersen (walt.petersen@msfc.nasa.gov)