Natural Harmonic Academic & Science->Electronics
Negative High Academic & Science->Electronics
No Headstone Academic & Science->Chemistry
Northern Hemisphere Academic & Science->Ocean Science

This is really a guess, for the only other term I found for NH was New Hampshire.

So many institutions use acronyms that have no meaning to anyone except to them and often under very narrow circumstances. If you were to ask someone from the same institution they would probably not know. The average native speaker of the language would have no idea, to them they would just be letters of the alphabet.

Unless the meaning becomes apparent from some other context on the document or another credible source there seems to be no harm in placing a note saying "meaning of acronym unknown", for that is what anyone reading the original document would also see... something that has no meaning to them.

Therefore it is an accurate translation despite that lapse.

The above, of course, after scratching our heads, researching and then coming to the conclusion that we cannot find a definitive answer.

Two possibilities which could have connection to teaching.

NH = Número de horas

I looked N.H up in the glossary yesterday and saw this question. I ended up figuring it out - in my case (similar context) it referred to the total number of class hours.