AISTropoAlert

Script to send a Mastodon alert when far away ships are seen using AIS ship reports

Copyright 2023 Jeffrey Luszcz

https://github.com/jeff-luszcz/AISTropoAlert

This script is licensed under the terms of the Apache 2.0 license

SPDX-License-Identifier: Apache License 2.0

About

This BASH script reads the input from a specific AIS-Catcher web server and checks to see if any reports are further than a user specified distance Seeing ships that are farther away than normal may indicate the Tropospheric Ducting or other long distance propagation at VHF/UHF frequencies is ongoing. This is of interest to Amateur Radio operators

See https://en.wikipedia.org/wiki/Tropospheric_propagation

An example Mastodon feed of output from this script for the Boston, MA, USA area can be found at https://mastodon.social/@AISTropoAlertBoston

Requirements

• This script requires the curl command line tool
• This script requires the jq command line tool
• This script requires AIS-Catcher to be running its web server interface
• This script requires AIS-Catcher to have Lat-Long flags or GPS enabled (e.g. share_loc on LAT lat.dddd LON long.dddd )
• A Mastodon account
• A Mastodon token

###Installation instructions;

Install AIS-Catcher if needed

Install jq if needed

sudo apt install jq

Install curl if needed

sudo apt install curl

Place the BASH script in a location on your file system (e.g. ~/bin/AISTropoAlert.sh)

Make the script executable

  chmod +x AISTropoAlert.sh

Replace the variable tokens in the AISTropoAlert.sh script with your information

1. DIST, a distance that represents far away ship reports (e.g. 10 or 20 miles or further)
2. URL, the URL of your AIS-Catcher web interface e.g. raspberrrypi.local:8383
3. MASTODON_URL, the URL of the posting API for your Mastodon server (e.g. https://mastodon.social/api/v1/statuses )
4. MASTODON_TOKEN, your secret Mastodon token, see instructions at here on how to generate a Token for yourself

Edit the status message with your location (default message says [replaceme])

Create a cronjob for this script

crontab -e

put in the following for your cron job

*/15 * * * * /home/yourname/bin/AISTropoAlert.sh

This will run this script every 15 minutes, edit yourname to be your user name or directory name

I recommend running AIS-Catcher as a service so it will always be running even after a reboot

When ships appear outside your distance limit, this script should make a posting to your Mastodon user The text that is posted can be customized by editing the status line as seen in the curl call in the script Te default status will post message in the format below:

Possible Tropo Near Boston: AIS reports from 7.064232 miles away seen 
at Fri 26 May 2023 12:00:02 PM EDT. Alerts triggered when ships seen over 2 miles away.

Future improvements

Show total ship count currently seen