Introduction

ModeS is a Mode-S and ADSB decoder written in Go. The project is a pure Go library, without dependency, that allows to quickly deformat and access the content of Mode-S message.

A small example application is provided that can be used to dump the content of a message. A more complete usage of the library is done in the sister project ModeS Viewer (https://github.com/twuillemin/modes-viewer).

The main goal of this project is exactitude, code clarity and completeness (if achievable).

Warning

This project is experimental and has bugs and issues. It should by no means be used in a context where one will have to rely (in the broadest meaning) on the provided information.

Format Supported

Mode-S

Downlink Format	Description
DF-0	Short air-air surveillance (ACAS)
DF-4	Surveillance, altitude reply
DF-5	Surveillance, identify reply
DF-11	All-call reply
DF-16	Long air-air surveillance (ACAS)
DF-17	Extended squitter (ADSB)
DF-18	Extended squitter/non transponder (ADSB)
DF-19	Military extended squitter
DF-20	Comm-B altitude reply
DF-21	Comm-B identify reply
DF-24	Comm-D (ELM)

ADSB

Code	BDS	Description	V0	V1	V2
0	?	No Position	OK	OK	OK
1	0,8	Aircraft Id	OK	OK	OK
2	0,8	Aircraft Id	OK	OK	OK
3	0,8	Aircraft Id	OK	OK	OK
4	0,8	Aircraft Id	OK	OK	OK
5	0,6	Surface position	OK	OK	OK
6	0,6	Surface position	OK	OK	OK
7	0,6	Surface position	OK	OK	OK
8	0,6	Surface position	OK	OK	OK
9	0,5	Airborne position	OK	OK	OK
10	0,5	Airborne position	OK	OK	OK
14	0,5	Airborne position	OK	OK	OK
12	0,5	Airborne position	OK	OK	OK
13	0,5	Airborne position	OK	OK	OK
14	0,5	Airborne position	OK	OK	OK
15	0,5	Airborne position	OK	OK	OK
16	0,5	Airborne position	OK	OK	OK
17	0,5	Airborne position	OK	OK	OK
18	0,5	Airborne position	OK	OK	OK
19	0,9	Airborne velocity	OK	OK	OK
20	0,5	Airborne position	OK	OK	OK
21	0,5	Airborne position	OK	OK	OK
22	0,5	Airborne position	OK	OK	OK
23		Reserved
24		Reserved
25		Reserved
26		Reserved
27		Reserved
28	6,1	Emergency report	OK	OK	OK
29	6,2	Target and status	_	OK	OK
30		Reserved
31	6,5	Operational status	OK	OK	OK

Comm-B

BDS	Description
0,0	No message available
0,7	Status
1,0	Data link capability report
1,7	Common usage GICB capability report
2,0	Aircraft identification
3,0	ACAS resolution advisory
4,0	Selected vertical intention
4,4	Meteorological routine air report
4,5	Meteorological hazard report
5,0	Track and turn report
6,0	Heading and speed report

ACAS

Code	Description
3,0	Resolution Advisory

Usage

Library

A full example using the library is given in the file main.go which goes from a single "line" of data received to outputting the detailed content.

A simple workflow can be:

package main

import (
	"encoding/hex"
	"fmt"

	adsbReader "github.com/twuillemin/modes/pkg/adsb/reader"
	"github.com/twuillemin/modes/pkg/bds/adsb"
	modeSMessages "github.com/twuillemin/modes/pkg/modes/messages"
	modeSReader "github.com/twuillemin/modes/pkg/modes/reader"
)

func main() {
	// Convert the string to its hexadecimal value
	binaryData, _ := hex.DecodeString("8D40768DEA3AB864013C088209CA")
	// Read to a Mode-S message if possible
	messageModeS, _ := modeSReader.ReadMessage(binaryData)
	// If the message has ADSB data
	if messageModeS.GetDownLinkFormat() == 17 {
		// Convert the message to its real type
		messageDF17 := messageModeS.(*modeSMessages.MessageDF17)
		// Read the ADSB content
		messageADSB, _ := adsbReader.ReadADSBMessage(
			adsb.ReaderLevel2,
			false,
			false,
			messageDF17.MessageExtendedSquitter)
		fmt.Print(messageADSB.ToString())
	}
}

which should hopefully print a report like:

Message:                                       29 - Target state and status information (BDS 6,2) [ADSB V2]
Subtype:                                       1 - Subtype 1
Selected Altitude Type:                        0 - MCP/FCU (Mode Control Panel / Flight Control Unit)
Selected Altitude :                            30016 feet
Barometric Pressure Setting (minus 800 mbars): 213.60000000000002 feet
Selected Heading :                             0 degrees
Navigation Accuracy Category - Position:       9 - EPU < 30 m - e.g. GPS (SA off)
Navigation Integrity Category - Baro:          1 - barometric altitude based on a Gilham input that has been cross-checked or on a non Gilham input
Source Integrity ReaderLevel:                  1 - SIL <= 1 * 10^-7 per flight hour or per sample
Source Integrity ReaderLevel Supplement:       0 - Probability of exceeding NIC radius of containment is based on "per hour"
Status of MCP/FPU Mode Bits:                   0 - no information provided for MCP/FCU mode bits
Autopilot Engaged:                             No information provided from MCP/FCU
VNAV Mode Engaged:                             No information provided from MCP/FCU
Altitude Hold Mode Engaged:                    No information provided from MCP/FCU
Approach Mode Engaged:                         No information provided from MCP/FCU
LNAV Mode Engaged:                             No information provided from MCP/FCU
TCAS / ACAS Operational :                      1 - TCAS/ACAS is operational

All the values printed are in fact extracted in their own structure, using either numerical value or enumeration when applicable. The ToString() function is present on most if not all the attributes and just builds a readable representation of the data otherwise accessible by the structure of the object.

Application

For extracting a single line content

go run cmd/main.go 8D40768DEA3AB864013C088209CA

For reading a file with multiple lines

go run cmd/main.go --file .\example\example2.txt

Application parameters

• file: The name of the file to process
• adsb_reader_level: The level of ADSB to use when reading ADSB data. From 0 to 2.

Sources

The main sources used are:

• ICAO, Annex 10, Volume IV (July 2014): Surveillance and Collision Avoidance System
• ICAO, Doc 9871, AN/460: Technical Provisions for Mode S Services and Extended Squitter

I am always open to add new valid sources of information. In particular, information about ACAS messages are welcome.

Versions

• v0.7.0:

  • Fix: Computation of ground distance
  • Add Computation of surface position

• v0.6.0:

  • Fix: Computation of position (CPR odd/even)
  • Add Computation of position from a reference point
  • Add support for Comm-B: 0,7; 1.7; 2,0; 4,0; 4,4; 4,5; 5.0 and 6.0
  • Cleaner reading of altitude data
  • The inference has been limited. The current Mode-S parser will now return all the possible message, leaving high-level inference to the client.
  • A lot of unitary tests and relative fixes

• v0.5.0:

  • Fix: Decoding of HCR and NIC for BDS 0,6
  • The ADSB reader level is no more inferred when possible, but always respect the given value
  • Cleaning of ADSB messages readers

• v0.4.0:

  • Mode ADSBSpy and "current state" of plane into a separate project

• v0.3.0:

  • Clean relation Format, SubType Version for ADSB messages
  • Bug fixes on some fields not well fetched from messages
  • Add unitary test on all main classes

• v0.2.0:

  • First public version

• v0.1.0: First version

License

Copyright 2019 Thomas Wuillemin thomas.wuillemin@gmail.com

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this project or its content except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.