Table 4.

Software states ordered by normal operating flow.

State	Description	Entered if
Start-up	Initialize peripherals and communications, check for errors, report status and enter Idle or Error state based on status	Power on
Idle	Instrument is ready to accept commands, while continuously monitoring position and system status	Either: Successful start-up Disarming profiler Reload ballast/arm complete
Reload ballast/arm	Reload actuator by melting used PCL material for easy removal. This is done by heating the heating element to a predefined temperature using a PID controller.	Received reload ballast/arm command and system state is idle
Armed	Ready the instrument for drop and flight by UAV: Read CTD sensors Update position based on GPS input Broadcast instrument status by LoRa Check for incoming commands Enter Dive state if dropped from UAV	State is idle and received arm command
Dive	Measures CTD downcast profile and continuously monitors if the dive should be aborted by setting Release ballast state if: Depth reached Leak detected Max dive time elapsed	Detected drop from UAV in arm state
Release ballast	Release ballast to start ascent by heating the heating element. Repeat if depth is not decreasing. Set ascent state when complete	Dive completed/aborted
Ascent	Measures CTD upcast profile and check if the instrument has reached the surface: Set state Release arm if surface reached Set state Low power surface if max ascent time elapsed	Decreasing depth detected after releasing ballast
Release arm	Release arms to enable pickup by heating the heating element. Sets state Surface when complete	Surface detected after ascent
Low power surface	Wait for reaching surface with non-essential systems shut down for low power consumption. Set state Release arm if surface reached	Surface not detected after ascent
Surface	Update position based on GPS input and broadcast it using LoRa radio along with system status	Release arm complete
Error	Broadcast error message while monitoring system status	Error detected