The AN/SSQ-536G is an air launched, bathythermograph which records water temperatures up to a depth of 800 meters  and  using a telemetry link, it radios the readings back to the launching aircraft. The G in the model number number denotes the case type. BT means BathyThermograph. X means eXpendable . The AN/SSQ-536G can profile a  800m water column within 10 minutes of water entry and its equipped with a probe release detector to ensure data integrity.

This bathythermograph  provides information on the sea temperature as its probe sinks, thus allowing the operator to create a water column temperature vs. depth profile to support acoustic propagation analysis.  It scuttles itself after 30 hours.

RF Channel: Between 136 and 173 MHz
Frequency spacing : ESP programmable.  99 uplink channels available. 37.5 KHz spacing.between channels. ESP means  Electronic Function Select for use prior
to loading and launching. This allows the operator to select thedesired  RF channel..
Telemetry frequency range: 1340 Hz to 2720 Hz
Power output: 0.25 watt.
Operational life: 12 minutes.
Battery type: Lithium
Length: 16.5 in.
Diameter: 4.875 inches
Weight : 8 pounds.
NATO stock number: 5845-21-914-479

Comment: At the start of a search,, an AN/SSQ-536 XBT bathythermograph was launched in order to give the crew some iidea of the water temperature.

 
Reference:

1) https://www.ultra.group/us/our-business-units/maritime/ultra-maritime-canada/sonobuoys/#acc-bathythermalsonobuoys
 

Sept 18/23