low-altitude vs low-level

low-altitude and low-level both are adjectives.

Word	Noun	Adjective	Verb	Adverb
low-altitude	No	Yes	No	No
low-level	No	Yes	No	No

As adjectives, low-altitude and low-level are synonyms defined as:

low-altitude (adjective)	low-level (adjective)
occurring at a relatively low altitude	lower in rank or importance
	at a low level in rank or importance
	occurring at a relatively low altitude
	not intense