WSR-88D GRAPHIC PRODUCT MESSAGES

This brief description of the contents of Radar Product Generator (RPG) files is intended as a guide only.

Message header block:
HWORD#    BYTE#          MEANING

1         1-2       Product code
2         3-4       Date of message (Days since 1 Jan 1970)
3-4       5-8       Time of message (seconds since midnight GMT)
5-6       9-12      Number of bytes in message
7         13-14     Numeric radar site ID
8         15-16     Numeric product destination ID
9         17-18     Number of data blocks in message

Product descript block:
HWORD#    BYTE#          MEANING

10        19-20     Block divider (FFFFx)
11-12     21-24     Radar latitude (deg N x 1000)
13-14     25-28     Radar longitude (deg E x 1000)
15        29-30     Radar height (ft MSL)
16        31-32     Product code (repeat of 1-2)
17        33-34     Operational mode (0=maintenance 1=clear 2=precip)
18        35-36     Volume coverage pattern (11,21,31,32)
19        37-38     "Sequence number"
20        39-40     Volume scan number
21        41-42     Volume scan start date (usually used as product tag)
22-23     43-46     Volume scan start time
24        47-48     Product generation date
25-26     49-52     Product generation time
27        53-54     Product dependent descriptor
28        55-56     Product dependent descriptor
29        57-58     Antenna elevation number
30        59-60     Product dependent descriptor
31-46     61-92     16 2-byte words, data level breakpoints
47        93-94     Product dependent descriptor (generally max value)
48        95-96     Product dependent descriptor
49        97-98     Product dependent descriptor
50        99-100    Product dependent descriptor
51        101-102   Product dependent descriptor
52        103-104   Product dependent descriptor
53        105-106   Product dependent descriptor
54        107-108   Number of map backgrounds preceding this message
55-56     109-112   Offset to start of symbology block (usually 60 bytes)
57-58     113-116   Offset to graphics block
59-60     117-120   Offset to tabular block

Product symbology block
HWORD#    BYTE#          MEANING

61        121-122   Block divider (FFFFx)
62        123-124   "Block identifier"
63-64     125-128   Length of symbology block
65        129-130   Number of layers in next block
66        131-132   Layer divider (FFFFx)
67-68     133-136   Length of next data layer

Data packet for 16-level radial graphic products:
HWORD#    BYTE#          MEANING

69        137-138   Identifier (AF1Fx)
70        139-140   Index of first range bin (?)
71        141-142   Number of range bins
72        143-144   I center of sweep
73        145-146   J center of sweep
74        147-148   Scale factor (number of screen pixcels per range bin)
75        149-150   Number of radials

For each radial:

     Number of run-length encoded (RLE) words in radial;
     Radial start angle (deg x 10);
     Radial angle delta (deg x 10);

     For each byte in radial, high 4 bits are length of run, low 4 bits are color
     level

Data packet for 16-level raster graphic products:
HWORD#    BYTE#          MEANING

69        137-138   Identifier (BA07x or BA0Fx)
70        139-140   Identifier (8000x)
71        141-142   Identifier (00C0x)
72        143-144   I coordinate start
73        145-146   J coordinate start
74        147-148   "X-scale INT" (apparently, 4 for 4-km mesh length)
75        149-150   "X-scale fractional" (apparently not used now)
76        151-152   "Y-scale INT" (apparently, 4 for 4-km mesh length)
77        153-154   "Y-scale fractional" (apparently not used now)
78        155-156   Number of rows
79        157-158   Packing descriptor

For each row:

     Number of run-length encoded (RLE) bytes in row, not including this byte;

     For each byte in row, high 4 bits are length of run, low 4 bits are color level

Data packet for 256-level DPA raster product:
(This is a portion of the national polar-stereographic HRAP grid)
HWORD#    BYTE#          MEANING

69        137-138   Identifier (0011x)
70        139-140   Height of grid box in decameters
71        141-142   Width of grid box in decameters
72        143-144   Number of boxes in a row (varies with latitude)
73        145-146   Number of rows

For each row:

     Number of run-length encoded (RLE) bytes in row, not including this byte;

     For each 2-byte word in row, high 8 bits are length of run, low 8 bits are data
     level (0-255).  0 is for no precip, 255 for missing values.
     Data values may be converted to rainfall amount by:

          DBA = -6.125 + (data value) ** 0.125
          RAINFALL (mm) = 10 ** (0.1*DBA)