INTERMAGNET V2.83 Coding Examples
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Coding Example for GOES Satellite
Each block of 126 bytes in IMFV2.83 must be encoded in 189 NESS-BINARY bytes (NESSbytes). NESS-BINARY breaks each pair of source bytes (word) into 3 NESSbytes. If the bits of the source word are B15-B0 with B15 the most significant, then these are placed right-justified in NESSbytes as follows: B15-B12 are in the first NESSbyte, B11-B6 are in the second NESSbyte and B5-B0 are in the third NESSbyte. Within NESSbytes, bit 6 is always set to 1 and bit 7 is set for odd parity. In the first NESSbyte, bits 5 and 4 are filled by sign extension, i.e. they take the same value as bit 3. As an example, consider the 16-bit source word h0C4E, d3150.
Step 1 - break into 3 formative NESSbytes.
byte 1: XXXX0000
byte 2: XX110001
byte 3: XX001110
Step 2 - sign extend in byte 1, bit 6=1, bit 7=odd parity.
NESSbyte 1:01000000
NESSbyte 2:11110001
NESSbyte 3:11001110
WORD: 0000 1100 01 00 1110
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NESSBYTES: 0100 0000 1111 0001 1100 1110
xxxx xx xx
After encoding, the 12-minute block is sent to the data collection platform (DCP) to be transmitted.
Consider the following data set:
date: March 23 1993 (day 082) time of first sample 12:00 Observatory identification: 04342275 (co-latitude 43.4° , longitude 227.5°) Sensor orientation is HDZF INTERMAGNET approved filtering No alert capability No BRMs Flag #1: 00111100 flag #2: 00000000 Minute values of C1, C2, C3, C4 209062 -56 423216 472036 209062 -52 423218 472038 209058 -46 423220 472038 209053 -49 423219 472035 209052 -51 423214 472030 209054 -55 423214 472031 209061 -56 423215 472035 209066 -55 423217 472039 209062 -52 423214 472034 209055 -54 423212 472030 209055 -52 423213 472030 209056 -50 423213 472031 Hex dump of IMFV2.83 binary of this 12-minute block: (126 characters) 52 00 2D 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A6 10 C8 1F 30 15 E4 13 A6 10 CC 1F 32 15 E6 13 A2 10 D2 1F 34 15 E6 13 9D 10 CF 1F 33 15 E3 13 9C 10 CD 1F 2E 15 DE 13 9E 10 C9 1F 2E 15 DF 13 A5 10 C8 1F 2F 15 E3 13 AA 10 C9 1F 31 15 E7 13 A6 10 CC 1F 2E 15 E2 13 9F 10 CA 1F 2C 15 DE 13 9F 10 CC 1F 2D 15 DE 13 A0 10 CE 1F 2D 15 DF 13 After conversion to NESS-BINARY for GOES satellite: (189 characters) 45 C8 40 C2 76 D9 C7 FE 73 FB E5 70 40 C2 F2 43 46 CE 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 7A 58 D0 7C E0 DF 43 40 D5 FE D0 D3 7A 58 D0 7C 70 DF 43 C8 D5 FE 58 D3 7A C8 D0 FD C8 DF 43 D0 D5 FE 58 D3 79 F4 D0 7C 7C DF 43 4C D5 FE 4C D3 79 70 D0 7C F4 DF C2 F8 D5 FD F8 D3 79 F8 D0 7C 64 DF C2 F8 D5 FD 7C D3 7A 54 D0 7C E0 DF C2 7C D5 FE 4C D3 7A 68 D0 7C 64 DF 43 C4 D5 FE DC D3 7A 58 D0 7C 70 DF C2 F8 D5 FE C8 D3 79 7C D0 7C 68 DF C2 70 D5 FD F8 D3 79 7C D0 7C 70 DF C2 F4 D5 FD F8 D3 7A 40 D0 7C F8 DF C2 F4 D5 FD 7C D3
Coding Example for METEOSAT Satellite
As the duration between two time slots on the METEOSAT satellite is one hour, five 12-minute blocks are chained and sent to the DCP for transmission. As a METEOSAT message is 640 bytes long, 10 bytes (hex00) are added to the end of the 630 bytes of the 12-minute blocks (5 X 126 bytes). Binary from IMFV2.83 format is sent to the DCP without any modification.
Consider the following data set:
date: March 23 1993 (day 082) time of first sample 12:00 Observatory identification: 04342275 (co-latitude 43.4° , longitude 227.5°) Sensor orientation is HDZF INTERMAGNET approved filtering No alert capability No BRMs Flag #1: 00111100 flag #2: 00000000 Minute values of C1, C2, C3, C4 Block # 1: minute 0-11 209062 -56 423216 472036 209062 -52 423218 472038 209058 -46 423220 472038 209053 -49 423219 472035 209052 -51 423214 472030 209054 -55 423214 472031 209061 -56 423215 472035 209066 -55 423217 472039 209062 -52 423214 472034 209055 -54 423212 472030 209055 -52 423213 472030 209056 -50 423213 472031 Block # 2: minute 12-23 209059 -45 423215 472034 209057 -45 423214 472032 209059 -40 423216 472035 209057 -42 423214 472032 209054 -40 423213 472030 209053 -42 423214 472030 209048 -45 423214 472028 209046 -47 423217 472030 209045 -45 423217 472030 209044 -46 423217 472029 209043 -44 423214 472026 209045 -43 423215 472028 Block #3 : minute 24-35 209050 -44 423215 472030 209056 -45 423217 472035 209064 -45 423218 472039 209072 -43 423217 472042 209073 -41 423216 472041 209069 -39 423216 472039 209063 -37 423215 472036 209059 -36 423216 472035 209054 -37 423216 472033 209051 -42 423215 472030 209046 -47 423215 472028 209045 -50 423216 472029 Block # 4: minute 36-47 209041 -56 423214 472025 209044 -58 423215 472027 209044 -60 423215 472027 209049 -57 423217 472031 209056 -54 423217 472035 209063 -48 423217 472038 209068 -45 423217 472040 209070 -42 423216 472040 209072 -40 423217 472042 209070 -38 423216 472040 209065 -40 423215 472037 209063 -41 423215 472036 Block # 5: minute 48-59 209067 -39 423217 472039 209064 -41 423216 472037 209059 -42 423215 472034 209058 -41 423215 472034 209061 -40 423214 472034 209063 -37 423215 472036 209060 -37 423215 472034 209060 -38 423213 472033 209063 -39 423213 472034 209063 -40 423212 472033 209068 -37 423215 472038 209071 -33 423217 472041 Hex dump of IMFV2.83 binary of these five 12- minute blocks: (5 * 126 + 10 trailing zeros = 640 characters) 52 00 2D 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A6 10 C8 1F 30 15 E4 13 A6 10 CC 1F 32 15 E6 13 A2 10 D2 1F 34 15 E6 13 9D 10 CF 1F 33 15 E3 13 9C 10 CD 1F 2E 15 DE 13 9E 10 C9 1F 2E 15 DF 13 A5 10 C8 1F 2F 15 E3 13 AA 10 C9 1F 31 15 E7 13 A6 10 CC 1F 2E 15 E2 13 9F 10 CA 1F 2C 15 DE 13 9F 10 CC 1F 2D 15 DE 13 A0 10 CE 1F 2D 15 DF 13 52 C0 2D 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A3 10 D3 1F 2F 15 E2 13 A1 10 D3 1F 2E 15 E0 13 A3 10 D8 1F 30 15 E3 13 A1 10 D6 1F 2E 15 E0 13 9E 10 D8 1F 2D 15 DE 13 9D 10 D6 1F 2E 15 DE 13 98 10 D3 1F 2E 15 DC 13 96 10 D1 1F 31 15 DE 13 95 10 D3 1F 31 15 DE 13 94 10 D2 1F 31 15 DD 13 93 10 D4 1F 2E 15 DA 13 95 10 D5 1F 2F 15 DC 13 52 80 2E 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 9A 10 D4 1F 2F 15 DE 13 A0 10 D3 1F 31 15 E3 13 A8 10 D3 1F 32 15 E7 13 B0 10 D5 1F 31 15 EA 13 B1 10 D7 1F 30 15 E9 13 AD 10 D9 1F 30 15 E7 13 A7 10 DB 1F 2F 15 E4 13 A3 10 DC 1F 30 15 E3 13 9E 10 DB 1F 30 15 E1 13 9B 10 D6 1F 2F 15 DE 13 96 10 D1 1F 2F 15 DC 13 95 10 CE 1F 30 15 DD 13 52 40 2F 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 91 10 C8 1F 2E 15 D9 13 94 10 C6 1F 2F 15 DB 13 94 10 C4 1F 2F 15 DB 13 99 10 C7 1F 31 15 DF 13 A0 10 CA 1F 31 15 E3 13 A7 10 D0 1F 31 15 E6 13 AC 10 D3 1F 31 15 E8 13 AE 10 D6 1F 30 15 E8 13 B0 10 D8 1F 31 15 EA 13 AE 10 DA 1F 30 15 E8 13 A9 10 D8 1F 2F 15 E5 13 A7 10 D7 1F 2F 15 E4 13 52 00 30 99 7F B3 B9 3C 00 B2 31 8E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 AB 10 D9 1F 31 15 E7 13 A8 10 D7 1F 30 15 E5 13 A3 10 D6 1F 2F 15 E2 13 A2 10 D7 1F 2F 15 E2 13 A5 10 D8 1F 2E 15 E2 13 A7 10 DB 1F 2F 15 E4 13 A4 10 DB 1F 2F 15 E2 13 A4 10 DA 1F 2D 15 E1 13 A7 10 D9 1F 2D 15 E2 13 A7 10 D8 1F 2C 15 E1 13 AC 10 DB 1F 2F 15 E6 13 AF 10 DF 1F 31 15 E9 13 00 00 00 00 00 00 00 00 00 00
Coding Example for GMS Satellite (Preliminary)
The GMS satellite system requires that DCP data transmission use a long preamble, recommends that the length of time for data block be at least 63 seconds, and that transmitted data conform to a specified character set. A base-44 coding algorithm was developed for converting binary data to the GMS character set. The coded data format follows:
Header (21 bytes coded)
length position frame Time day of the year 12 bit 3/4 word 0 word-0.75 minute of the day 12 bit 3/4 word 0.75word-1.5 offset C1 1/2 word 1.5 word-2.0 offset C2 1/2 word 2.0 word-2.5 offset C3 1/2 word 2.5 word-3.0 offset C4 1/2 word 3.0 word-3.5 Flag #1 & #2 1 word 3.5 word-4.5 station ID colatitude 12 bit 3/4 word 4.5 word-5.25 longitude 12 bit 3/4 word 5.25word-6.0 -18byte (CR-CR-LF)-21byte
Free Space (27 bytes coded)
D1 Indices and Baseline control 1/2 word 6.0 word-6.5
:
D18 " " " " 1/2 word 15.5 word-15.0 -48byte
(CR-CR-LF) -51byte
Minute Values (157 bytes coded)
C1 for t+0 minute 1 word 15.0 word-16.0 -54byte
C2 for t+0 minute 1 word 16.0 word-17.0 -57byte
C3 for t+0 minute 1 word 17.0 word-18.0 -60byte
C4 for t+0 minute 1 word 18.0 word-19.0 -63byte
:
C4 for t+4 minute 1 word 34.0 word-35.0 -111byte
(CR-CR-LF)-114byte
C1 for t+5 minute 1 word 35.0 word-36.0 -117byte
:
C4 for t+9 minute 1 word 54.0 word-55.0 -174byte
(CR-CR-LF)-177byte
C1 for t+10 minute 1 word 55.0 word-56.0 -180byte
:
C1 for t+11 minute 1 word 59.0 word-60.0 -192byte
C2 for t+11 minute 1 word 60.0 word-61.0 -195byte
C3 for t+11 minute 1 word 61.0 word-62.0 -198byte
C4 for t+11 minute 1 word 62.0 word-63.0 -201byte
CRC 1 word 63.0 word-64.0 -204byte
('='-CR-CR-LF)-208byte
Time framing for GMS
A multiple data transmission (12-minute data block repeated 3 times) may be used to satisfy the GMS minimum block transmission time of approximately 63 seconds. The time framing for GMS would be:
no-signal carrier 5.0 second : 5.0 sec bit synchronization 2.5 : 7.5 word synchronization 0.15 : 7.65 address 0.31 : 7.96 first (64*3+16-1)*8/100 16.56 :24.52 (177 bytes) second (64*3+16-1)*8/100 16.56 :41.08 (177 bytes) last (64*3+16)*8/100 16.64 :57.72 (178 bytes) EOT-EOT-EOT 0.24 :57.96
The following table shows time slots assigned to DCPs. Each table line represents 60 seconds, the station ID is placed at the beginning of a data transmission block, '....' is for the no-signal (carrier only) period, '--' is for synchronization sequence, and '==' is for the data block. Assigned time slots for the GMS coding would allow 58 seconds per transmission and 7 seconds guard time. This would allow 11 observatories to transmit every 12 minutes.
min sec0....*....1....*....2....*....3....*....4....*....5....*.... 12*(n) .....--M01================================================__ +01 _____.....--M02============================================= +02 ===_______.....--M03======================================== +03 ========_______.....--M04=================================== +04 =============_______.....--M05============================== +05 ==================_______.....--M06========================= +06 =======================_______.....--M07==================== +07 ============================_______.....--M08=============== +08 =================================_______.....--M09========== +09 ======================================_______.....--M10===== +10 ===========================================_______.....--M11 +11 ================================================____________ 12(n+1).....--M01================================================__ :
Base-44 Coding for GMS
The characters used on the GMS system are: LF CR SP ' ( ) + , - . / 0 1 2 3 4 5 6 7 8 9 : = ? A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (TOTAL 50). The base-44 character set is shown below. Each IMFV2.81 data block is encoded by dividing the data block into 16-bit integers. Signed integers are represented by 2's complement. Each integer value is converted to 3 base-44 numbers, <n1,n2,n3>, the most significant being n1 and the least significant n3. Each base-44 number may be represented by a base-44 character from the table below. Example conversions are shown below.
Digit Base-44 Digit Base-44 Digit Base-44 < 0> 0 <15> F <30> U < 1> 1 <16> G <31> V < 2> 2 <17> H <32> W < 3> 3 <18> I <33> X < 4> 4 <19> J <34> Y < 5> 5 <20> K <35> Z < 6> 6 <21> L <36> ( < 7> 7 <22> M <37> ) < 8> 8 <23> N <38> + < 9> 9 <24> O <39> ,(comma) <10> A <25> P <40> -(hyphen) <11> B <26> Q <41> .(period) <12> C <27> R <42> :(colon) <13> D <28> S <43> ? <14> E <29> T
Example Base-44 Conversions
decimal base-44 base-44
number number char
0 <0,0,0> 000
1 <0,0,1> 001
43 <0,0,43> 00?
44 <0,1,0> 010
32767 <16,40,31> G-V
-1 <43,43,43> ???
-44 <43,43,0> ??0
-1935 <43,0,1> ?01
-32768 <27,3,12> R3C
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