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NIDS Format

Nexrad Level 3 Data Format


NIDS data is a format for displaying Nexrad data.  NIDS data is separated into the following blocks:

Tables:


1. Message Header Block

Halfword Name Description
01 Message Code See message code table below
02 Date of Message Number of days since 1 Jan 1970
03 Time of Message (MSW) Number of seconds since midnight
04 Time (LSW)  
05 Length of Message (MSW) Number of bytes in message including header
06 Length (LSW)  
07 Source ID  
08 Destination ID  
09 Number of Blocks 1 (Header Block) + number of blocks in message

2. Product Description Block

10 Divider Integer value -1
11 Latitude of Radar (MSW) Latitude*1000, + is north
12 Latitude (LSW)  
13 Longitude of Radar (MSW) Longitude*1000, + is east
14 Longitude (LSW)  
15 Height of Radar Feet above sea level
16 Product Code See message code table below
17 Operational Mode 0=Maintenance, 1=Clear air, 2=Precipitation/Severe weather
18 Volume Scan Pattern RDA volume coverage pattern
19 Sequence Number Sequence number of the request that generated the product
20 Volume Scan Number Counter, cycles 1 to 80
21 Volume Scan Date  
22 Volume Scan Time (MSW)  
23 Time (LSW)  
24 Product Generation Date  
25 Product Generation Time (MSW)  
26 Time (LSW)  
27 P1 Product specific codes, see product codes below
28 P2  
29 Elevation Number Elevation scan within volume scan
30 P3  
31 Data 1 Threshold Data threshold values, see threshold discussion below
32 Data 2 Threshold  
33 Data 3 Threshold  
34 Data 4 Threshold  
35 Data 5 Threshold  
36 Data 6 Threshold  
37 Data 7 Threshold  
38 Data 8 Threshold  
39 Data 9 Threshold  
40 Data 10 Threshold  
41 Data 11 Threshold  
42 Data 12 Threshold  
43 Data 13 Threshold  
44 Data 14 Threshold  
45 Data 15 Threshold  
46 Data 16 Threshold  
47 P4  
48 P5  
49 P6  
50 P7  
51 P8  
52 P9  
53 P10  
54 Number of Maps  
55 Offset to Symbology Block (MSW) Number of halfwords (2 bytes) from start of product to block
56 Offset (LSW)  
57 Offset to Graphic Block (MSW)  
58 Offset (LSW)  
59 Offset to Tabular Block (MSW)  
60 Offset (LSW)  

3. Product Symbology Block

The Symbology Block has a header plus a number of data layers.  These layers can be graphical such as radial and rastor scan data or could be textual or symbolic such as TVS locations.

01 Divider  
02 Block ID Integer value 1
03 Length of Block (MSW) Length in bytes
04 Length (LSW)  
05 Number of Layers  

Symbology Layer

Within the layer, there are a number of data packets which describe the type of information to be plotted.

01 Divider  
02 Length of Block (MSW) Length in bytes
03 Length (LSW)  
04-## Display Data Packets  

3.1. Radial Data Packet

Radial data contains values for each bin within a particular radial.  Each radial is defined by a start and end angle and by distance.  There are multiple radials that define a full scan.

01 Packet Code Hex "AF1F"
02 Index of First Range Bin  
03 Number of Range Bins Number of bins in each radial
04 I Center of Sweep Center point location in a -2048 to 2047 coordinate region(mostly 0,0)
05 J Center of Sweep  
06 Scale Factor Number of pixels per range bin
07 Number of Radials  

Individual Radials

Each radial contains Run Length Encoded (RLE) values.

01 Number of RLE Halfwords RLE data always padded to even halfword boundary
02 Radial Start Angle Angle*10, scan direction is always clockwise
03 Radial Angle Delta Angle*10
04 Run0 Code0 Run1 Code1 Run is 4 bit value for number of bins for this value
05 Run2 Code2 Run3 Code3 Code is 4 bit value (0-15) for the value within the run
06-## Run Codes Repeated for entire radial
## RunN CodeN 00 00  

3.2. Raster Data Packet

Raster data is pixelized data defined by rows and columns.

01 Packet Code Hex "BA0F" or "BA07"
02 Op Flags Hex "8000"
03 Op Flags Hex "00C0"
04 I Start Coordinate Start coordinate on -2048 to 2047 coordinate system
05 J Start Coordinate  
06 X Scale (INT) Reserved
07 X Scale (FRACT)  
08 Y Scale (INT) Reserved
09 Y Scale (FRACT)  
10 Number of Rows  
11 Packing Descriptor Always 2

Individual Rows

Each row contains Run Length Encoded (RLE) values.

01 Number of Bytes in Row RLE data always padded to even halfword boundary
02 Run0 Code0 Run1 Code1 Run is 4 bit value for number of bins for this value
03 Run2 Code2 Run3 Code3 Code is 4 bit value (0-15) for the value within the run
04-## Run Codes Repeated for entire row
## RunN CodeN 00 00  

3.3. Vector Arrow Packet

These define the location and size of vector arrows to be plotted.

01 Packet Code = 5 Hex "5"
02 Length of Data In bytes

Individual Vectors

Each arrow is 5 halfwords and is repeated until byte length.

01 I Coordinate  
02 J Coordinate  
03 Direction of Arrow In degrees
04 Arrow Length In pixels
05 Arrow Head Length In pixels

3.4. Wind Barb Packet

These define the location and size of wind barbs to be plotted.

01 Packet Code = 4 Hex "4"
02 Length of Data In bytes

Individual Barbs

Each barb is 5 halfwords and is repeated until byte length.

01 Value Color value (0-5) representing RMS variation of wind speed
02 I Coordinate  
03 J Coordinate  
04 Direction of Wind In degrees
05 Wind Speed  

3.5. Digital Precipitation Array Packet

01 Packet Code = 17 Hex "11"
02 Op Flags Reserved
03 Op Flags Reserved
04 Number of LFM Boxes in Row  
05 Number of Rows  

Individual Rows

Each row contains Run Length Encoded (RLE) values.

01 Number of Bytes in Row RLE data always padded to even halfword boundary
02 Run0 Code0 Run is 8 bit value for number of bins for this value
03 Run1 Code1 Code is 8 bit value (0-255) for the value within the run
04-## Run Codes Repeated for entire row
## RunN CodeN  

3.6. Unlinked Vector Packet

This is a set of unlinked vectors that plot disconnected lines on the plot.

01 Packet Code = 7 Hex "7"
02 Length of Data In bytes
03 Vector 1, I Start Vector 1 start and end coordinates
04 Vector 1, J Start  
05 Vector 1, I End  
06 Vector 1, J End  
07 Vector 2, I Start Vector 2 start and end coordinates
08 Vector 2, J Start  
09 Vector 2, I End  
10 Vector 2, J End  
11-## Repeated Vectors  

3.7. Valued Unlinked Vector Packet

This is a set of unlinked vectors that plot disconnected lines on the plot. This contains a value level for coloring.

01 Packet Code = 7 Hex "7"
02 Length of Data In bytes
03 Value Color level of vector
04 Vector 1, I Start Vector 1 start and end coordinates
05 Vector 1, J Start  
06 Vector 1, I End  
07 Vector 1, J End  
08 Vector 2, I Start Vector 2 start and end coordinates
09 Vector 2, J Start  
10 Vector 2, I End  
11 Vector 2, J End  
12-## Repeated Vectors  

3.8. Text and Symbol Packet

This is for plotting text and symbols.

01 Packet Code = 1 Hex "1"
02 Length of Data In bytes
03 I Start Vector 1 start and end coordinates
04 J Start  
05 Char1 Char2 Each character in string
06 Char3 Char4  
07-## Repeated  
## CharN-1 CharN  

3.9. Valued Text and Symbol Packet

This is for plotting text and symbols.  A color value is also listed

01 Packet Code = 1 Hex "1"
02 Length of Data In bytes
03 Value of String  
04 I Start Vector 1 start and end coordinates
05 J Start  
06 Char1 Char2 Each character in string
07 Char3 Char4  
08-## Repeated  
## CharN-1 CharN  

A. Message Codes

Code Name Resolution Range Levels Description
16 Base Reflectivity .54nm x 1deg 124 8 Radial Image
17 Base Reflectivity 1.1nm x 1deg 248 8 Radial Image
18 Base Reflectivity 2.2nm x 1deg 248 8 Radial Image
19 Base Reflectivity .54nm x 1deg 124 16 Radial Image
20 Base Reflectivity 1.1nm x 1deg 248 16 Radial Image
21 Base Reflectivity 2.2nm x 1deg 248 16 Radial Image
22 Base Velocity .13nm x 1deg 32 8 Radial Image
23 Base Velocity .27nm x 1deg 62 8 Radial Image
24 Base Velocity .54nm x 1deg 124 8 Radial Image
25 Base Velocity .13nm x 1deg 32 16 Radial Image
26 Base Velocity .27nm x 1deg 62 16 Radial Image
27 Base Velocity .54nm x 1deg 124 16 Radial Image
28 Base Spectrum Width .13nm x 1deg 32 8 Radial Image
29 Base Spectrum Width .27nm x 1deg 62 8 Radial Image
30 Base Spectrum Width .54nm x 1deg 124 8 Radial Image
35 Composite Reflectivity .54nm x .54nm 124 8 Rastor Image+Alphanumeric Data
36 Composite Reflectivity 2.2nm x 2.2nm 248 8 Rastor Image+Alphanumeric Data
37 Composite Reflectivity .54nm x .54nm 124 16 Rastor Image+Alphanumeric Data
38 Composite Reflectivity 2.2nm x 2.2nm 248 16 Rastor Image+Alphanumeric Data
41 Echo Tops 2.2nm x 2.2nm 124 16 Rastor Image
48 VAD Wind Profile 5knots NA 5 Alphanumeric+Wind Barbs
55 Storm Relative Mean Radial Velocity .27nm x 1deg 27 16 Radial Image (Region)
56 Storm Relative Mean Radial Velocity .54nm x 1deg 124 16 Radial Image (Map)
57 Vertically Integrated Liquid 2.2nm x 2.2nm 124 16 Rastor Image
63 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 1 average)
64 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 2 average)
65 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 1 maximum)
66 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 1 maximum)
74 Radar Coded Message        
75 Free Text Message        
78 Surface Rainfall Accumulation - 1hr 1.1nm x 1.1nm 124 16 Rastor Image
79 Surface Rainfall Accumulation - 3hr 1.1nm x 1.1nm 124 16 Rastor Image
80 Storm Total Rainfall Accumulation 1.1nm x 1.1nm 124 16 Rastor Image
81 Hourly Digital Precipitation Array 1/40 LFM 124 100max Rastor Image on LFM grid
89 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 3 average)
90 Layer Composite Reflectivity 2.2nm x 2.2nm 124 8 Rastor Image (Layer 3 maximum)

B. Product Specific Codes

Product Name P3 (HW#30) P4 (HW#47) P5 (HW#48) P6 (HW#49)
Base Reflectivity Elevation Angle*10 Maximum Reflectivity    
Base Velocity Elevation Angle*10 Max Negative Velocity Max Positive Velocity  
Base Spectrum Width Elevation Angle*10 Maximum Width    
Composite Reflectivity   Maximum Reflectivity    
Echo Tops   Maximum Top    
Hourly Digital Precipitation   Max Rainfall Accumulation    
Layer Composite Reflectivity   Maximum Reflectivity Bottom of Layer (1000ft) Top of Layer
Storm Rel Mn Velocity Elevation Angle*10 Max Negative Velocity Max Positive Velocity  
Surface Rainfall Accumulation   Max Rainfall Accumulation    
Storm Total Rainfall   Max Rainfall Accumulation Begin Julian Date (day) Begin Time (min)
Vertically Integrated Liquid   Max VIL    

 

Product Name P7 (HW#50) P8 (HW#51) P9 (HW#52) P10 (HW#53)
Storm Total Rainfall End Julian Date (day) End Time (min)