It detects its echo on substrata or foundations (5)
I believe the answer is:
sonar
'it detects' is the definition.
(sonar detects things using soundwaves)
'its echo on substrata or foundations' is the wordplay.
'its' becomes 'nos' (I can't justify this - if you can you should give a lot more credence to this answer).
'echo' shows that the letters should be reversed in order (I've seen 'echoing' mean this (echo can mean to reflect or bounce back)).
'on' means one lot of letters go next to another.
'foundations' suggests the final letters (I've seen 'foundation' mean this (the letter at the bottom of the word)).
The last letters of 'substrata or' are 'ar'.
'nos' back-to-front is 'son'.
'son'+'ar'='SONAR'
Can you help me to learn more?
(Other definitions for sonar that I've seen before include "Underwater detection device" , "System for locating underwater objects" , "location device" , "Detection system at sea" , "Method of echolocation" .)