# What is this device on top of this SUV? **URL:** \ **Category:** Factual Questions\ **Created:** [December 9, 2022, 1:10pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260 "2022-12-09T13:10:32Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [December 9, 2022, 1:10pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/1 "2022-12-09T13:10:32Z")
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? [![](https://i.imgur.com/hWXQSAW.jpeg) ](https://i.imgur.com/hWXQSAW.jpeg) (sorry, this is the best picture I could get of it; I was driving at the time) ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [December 9, 2022, 1:23pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/2 "2022-12-09T13:23:49Z")
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: > **[Air and Wind Speed, Meteorology, Weather Station HD2003 - 3-Axis Ultrasonic...](https://www.deltaohm.com/product/hd2003-3-axis-ultrasonic-anemometer-2/)** > > Cerchi Air and Wind Speed, Meteorology, Weather Station? Scopri le caratteristiche di HD2003 - 3-Axis Ultrasonic Anemometer di Delta OHM ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [December 9, 2022, 1:33pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/3 "2022-12-09T13:33:10Z")
Interesting. Thanks. I assumed it was something like that. Or, that there were aliens in that thing. 😉 ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [December 9, 2022, 3:53pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/4 "2022-12-09T15:53:44Z")
I hope you were wearing your tinfoil hat when you drove past… ---
**Author:** ![Limmin](https://avatars.discourse-cdn.com/v4/letter/l/f04885/32.png) [@Limmin](https://boards.straightdope.com/u/Limmin)\ **Post date:** [December 9, 2022, 3:56pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/5 "2022-12-09T15:56:23Z")
Ok…why? Why put this particular equipment on top of a US Gov’t SUV? I can’t come up with an explanation. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [December 9, 2022, 3:57pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/6 "2022-12-09T15:57:49Z")
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. ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [December 9, 2022, 3:59pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/7 "2022-12-09T15:59:40Z")
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. ---
**Author:** ![Limmin](https://avatars.discourse-cdn.com/v4/letter/l/f04885/32.png) [@Limmin](https://boards.straightdope.com/u/Limmin)\ **Post date:** [December 9, 2022, 4:01pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/8 "2022-12-09T16:01:16Z")
Maybe… its function it to help calibrate the weather stations at airports? ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [December 9, 2022, 9:40pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/9 "2022-12-09T21:40:29Z")
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. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [December 9, 2022, 10:09pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/10 "2022-12-09T22:09:19Z")
> [@enipla](#): > > Please be careful when taking pictures while moving in you car. 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. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [December 9, 2022, 10:17pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/11 "2022-12-09T22:17:12Z")
“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.” ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 10, 2022, 3:15am UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/12 "2022-12-10T03:15:49Z")
Well if you were in the UK it’d be obvious what that was: The cat detector van. ---
**Author:** ![Spiderman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiderman/32/230_2.png) [@Spiderman](https://boards.straightdope.com/u/Spiderman)\ **Post date:** [December 10, 2022, 5:07am UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/13 "2022-12-10T05:07:21Z")
> [@DCnDC](#): > > Or, that there were aliens in that thing. 😉 Given that the _very next_ post > [@Marvin\_the\_Martian](#): > > I hope you were wearing your tinfoil hat when you drove past… is by an alien you have enough info to know which [governmental agency](https://m.media-amazon.com/images/M/MV5BOTlhYTVkMDktYzIyNC00NzlkLTlmN2ItOGEyMWQ4OTA2NDdmXkEyXkFqcGdeQXVyNTAyODkwOQ@@._V1_.jpg) the vehicle belongs to. 👽 ---
**Author:** ![Shoeless](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shoeless/32/7099_2.png) [@Shoeless](https://boards.straightdope.com/u/Shoeless)\ **Post date:** [December 10, 2022, 5:38pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/14 "2022-12-10T17:38:03Z")
> [@LSLGuy](#): > > Well if you were in the UK it’d be obvious what that was: The cat detector van. _Loony_ detector van… ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 10, 2022, 6:01pm UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/15 "2022-12-10T18:01:17Z")
> [@Dewey\_Finn](#): > > 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. Vehicle manufacturers and vehicle emissions enforcement agencies (such as EPA and **[CARB](https://en.wikipedia.org/wiki/California_Air_Resources_Board)**) 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](https://michelinpg.com/engineering-services/)** 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](https://www.google.com/maps/@42.5835472,-83.683335,5741m/data=!3m1!1e3?hl=en)**), 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. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [December 11, 2022, 12:06am UTC](https://boards.straightdope.com/t/what-is-this-device-on-top-of-this-suv/976260/16 "2022-12-11T00:06:15Z")
> [@Machine\_Elf](#): > > Vehicle manufacturers and vehicle emissions enforcement agencies (such as EPA and **[CARB](https://en.wikipedia.org/wiki/California_Air_Resources_Board)**) 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” Where I live, they just put camouflage on new car models and drive them over the continental divide. I see them all the time.