Javier,
What these figures refer to is bathythermal buoys. The SSQ36 dropped to a depth of 1000ft at a known descent rate. The surface unit of the buoy then transmitted the temperature back to the aircraft as the temperature unit descended. These buoys were later replaced with buoys that went down to 1500ft.
AMBTN OUT (55/73/115/65/305/58/850/55/1150/53) refers to:
At 55Hz - Ambient noise is 73dB
115Hz - Ambient noise is 65dB and so on....
These readings would be taken from most other types of passive sonobuoy but the SSQ36 was not able to provide ambient noise readings.
Hope this helps,
Ping