Driving home yesterday I found myself driving next to this SUV. It had “US Government” plates, and this strange device mounted on the roof. The vehicle was unaccompanied.
What did I see?
(sorry, this is the best picture I could get of it; I was driving at the time)
Looks like wind speed direction and other quantities being measured. Front unit is an ultrasonic speed and direction unit, and the rear one probably does temperature, barometric pressure etc.
Nearest I could find with a quick search was this:
Interesting. Thanks. I assumed it was something like that. Or, that there were aliens in that thing. 
I hope you were wearing your tinfoil hat when you drove past…
Ok…why? Why put this particular equipment on top of a US Gov’t SUV? I can’t come up with an explanation.
Perhaps the vehicle belongs to the National Weather Service, or another government agency interested in the weather? The EPA, for instance, might be interested in wind and air monitoring.
Just after taking that photo it turned right, and that road goes directly to the College Park Airport, which may or may not be any sort of clue. Or maybe just a coincidence.
Maybe… its function it to help calibrate the weather stations at airports?
Not sure what that is, I think we have some good ideas though. At first I thought it may be a device to search for ELT’s Emergency Locator Transmitters carried on all general aviation aircraft.
Please be careful when taking pictures while moving in you car. Generally not a very good idea.
Yes. Back when Pokemon Go was a a thing, there was a freeway electronic sign that warned not to take pictures of Pokemons while driving. I thought it was such a funny sign that I took a picture of it.
Hey, the sign only mentioned Pokemons.
“How did you get onto that highway accident?”
“I was taking a picture of a sign that warned me not to take pictures from a moving car.”
Well if you were in the UK it’d be obvious what that was: The cat detector van.
Given that the very next post
is by an alien you have enough info to know which governmental agency the vehicle belongs to. 
Loony detector van…
Vehicle manufacturers and vehicle emissions enforcement agencies (such as EPA and CARB) routinely test vehicles on chassis dynamometers in test cells. To accurately mimic the real-world aero/tire drag effects of the vehicle being tested, the dyno is programmed with a set of “road load coefficients” that are derived from a real-world coast-down test that takes place under carefully specified conditions. The coast-down test involves accelerating the vehicle on a straight flat paved surface to some target speed and then putting it in neutral and recording velocity versus time as the speed gradually decays due to drag. The test is then repeated in the opposite direction to help cancel out the effects of ambient wind and slope. There’s a max allowable limit to the ambient wind, and specific requirements for measuring ambient wind speed during the test, either at a fixed location at the test site or on the vehicle itself. I don’t recall whether the standard allows more ambient wind if you’re measuring on the vehicle itself or not, but since measuring on the vehicle tends to be more difficult, and people do it anyway, there must be some benefit. If you scroll down on this site to the line for “SAE J2265/J1263 Coast Down/Road Load Testing”, you’ll see a picture of a car that’s been outfitted with an anemometer mounted on a boom to get it out into the “clean” air well in front of the car. I don’t recall whether the testing standard allows an ultrasonic sensor to be mounted on top of the vehicle like in the OP’s photo, but it’s possible.
The car pictured in the OP may be one that’s on its way to a coast-down test. The test site can be a manufacturer’s test track (there are several in SE Michigan, example here), or it can just be an airport runway. This would be consistent with the OP’s report that the vehicle was last seen headed for the College Park airport.
Where I live, they just put camouflage on new car models and drive them over the continental divide. I see them all the time.
