The Penetration Depth of a Densiometer sound a bit large. OTOH that is IIRC also it's total range. And 1500km is very close to a planet. Unless you are using that thing on a Spyship and find a way for that spyship to circle the planet often enough for a complete scan WITHOUT making the locals suspicious(1). Otherwise you will likely find the DMS the Viking way(2)
Or you put it in the back of a truck, and drive the truck around on (or just above) the planet's surface.
GT Starships lists the standard size as 1 space, and the mass as 12.5 tons. Do this for a couple of weeks, and send your recordings off to Tozjabr HQ. Coming up with a plausible situation for offworlders to be driving a vehicle around for two weeks... I'd say that's another roleplaying opportunity. How many PCs would be slavering at the opportunity to figure out a way to smuggle in a grav vehicle that has super-secret spy gear in the back, and then get to run around in it for weeks?
The rules also say that you can build more powerful units; for each +6 to scan, the range, cost, space, and mass all go up by 10. You quickly get into something that you're not going to be able to hide in a ground vehicle (or grav vehicle, but you take my point), but it's easy to get a piece of gear into a good-sized freighter that will reach all the way from geostationary to the planetary mantle. Dock at the highport, keep Customs out of that cargo bay, and give your crew "two weeks vacation -- except for the anchor watch, or course." You could even claim to be doing maintenance, as long as you keep nosy Starport Authority techs from finding out what you're actually doing (or you could actually
do some maintenance on other areas of the ship).
For that matter, you could just decide to come to a downport and park the ship. Arranging something beforehand to require your ship and its crew to land should be simple. Complete the rest of the task as above.
Without recon efforts, it's going to be difficult to attack a deep meson gun site, but with some work (and long-ranged scanners) beforehand, you can get some idea of the location of the sites. It won't help in case of a lightning attack, but very little will.