low-level vs low-altitude

low-level and low-altitude both are adjectives.

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

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

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