New to chasing: looking for a mobile mesonet setup

[Dustin Janise]

Whats a good Mobile Mesonet setup for a someone just getting into Chasing? I'm don't need the best of the best, just want to gather data while I'm out chasing.

I'm looking at a Davis Vantage Vue, with the Envoy and Weatherlink software. But I'd like to view my other options as well.

 

[Colby Ward]

I just purchased the Vantage Vue with the mobile mount for my Prius this week. I have not yet gotten the Envoy but so far the unit works great. I did have to invest some money into a roof rack system as well. The mobile mount has a magnetic base but it also must be strapped down so make sure you check into that if you do not already have one on your vehicle.
It was the best option I could find although there are other more expensive options now available.

 

[D. McGee]

Are you using the one from ambient weather?

 

[Colby Ward]

Yes, that's the one!

 

[Dustin Janise]

I was looking at that mobile mount from ambient weather, but I don't like the fact that it is only 14" above the roof which could cause some inaccurate readings.

 

[Colby Ward]

It may not be perfect but the readings so far have been very good. I have not noticed any strange readings thus far. I just wish I had some storms to test it out on. Another advantage is that it is simple to put together and install. Also, when I'm not chasing I can take it off the roof in about 3 minutes and put it back on in the same amount of time. It also fits perfectly in the back seat for the longer trips.

 

[Sean Waugh]

There are a variety of questions and answers that can go on here, but there are a few simple things that you need to consider first. First and foremost is WHY you want to put all this equipment on your car. It seems to me, that someone that is just getting into chasing should be more concerned with learning how to chase rather than being concerned about collecting data. Granted yes, there are a variety of benefits of having particular pieces of equipment on your car, but it comes at an added cost of difficultly. Maintaining your equipment, making sure that it isn't going to go flying off your car at 70 mph, setting everything up properly, it's a lot to deal with when you're still trying to learn. You don't need a bunch of equipment on your car to make you a chaser, unless you're only doing it for the attention in which case you're doing it for the wrong reasons.

Secondly, if you are dead set on have the equipment, then you need to decide what you want it for. If you just want it to kinda play around with and don't want to spend too much time or money on it, then there are a variety of options available. If you're a little more serious about things, and actually care about about the data you're collecting, then there are several things that you need to consider that are going to complicate things more.

And for the record, it's hard to say with complete confidence that ANY instrument is accurate. It's a loaded statement. Even so called "professional" sites like the OK Mesonet have their share of issues that need to be considered. Of course this is all my own opinion, you can take it however you want.

 

[Dan Robinson]

Most of the consumer-grade stations (Davis and OS for example) do not hold up well to mobile use, specifically the anemometer cups. Though, they can be replaced if they break. For practical chasing purposes, temperature and dewpoint have been helpful to have. From a hobbyist perspective, I don't think it's unreasonable to want to collect personal data during a storm chase, a highly meteorologically-relevant activity.

I've always tried to understand the criticism of non-research grade mobile instrument use, so far without success. When does any buyer and user of a Davis, Kestrel or OS unit contribute to any meaningful data collection for research or other purposes? Most home-based installs are no better in terms of data integrity than using one on a car, yet lack the same critical outcry. I would venture to say that a house presents more aerodynamic and thermal interference than a vehicle for wind and temperature measurements. Furthermore, how many $300 Oregon Scientific units are on properly isolated 2-meter towers? These consumer-grade instruments aren't made with VORTEX aspirations in mind - they are hobbyist gadgets, made for that purpose and nothing more. I am curious to know what the true indictment against vehicle use is as opposed to everyone else who has one installed on their back porch. I just never see scathing essays about Grandma's data from her Davis in the backyard flower garden being useless to researchers, and that all she really cares about is getting attention from the other members of the local church ladies' auxiliary. I apologize for the slightly opinionated tone, but wonder if someone could offer some enlightenment that I'm not getting.

 

[Dustin Janise]

My goal is just to gather data while chasing. I'm in to way, shape, or form expecting to get V2 grade data. I just want to know what the wind, temp, dew point, and barometric pressure is doing while I'm chasing.

 

[David Drummond]

I like having my Davis station on there, because I really like knowing the exact temp/dewpoint at any point prior to and during the chase. I like the anemometer because, frankly, I suck at estimating wind speeds for reporting purposes, and the rain gauge is great for rainfall rates, as that can be important for flash flooding potential, especially out here in west Texas, and the NWS offices out here like that info.

I'd love to have a full RM Young setup to log the data, but my attempts and inquiries on designs, blueprints or any help in building one have mostly gone unanswered from those that know how to build such things.

As a side note Dan, the new design they have for the replacement wind cups on the Davis is far superior to the past ones. My current cup set has been on there for over a year now without breaking when passing a truck like the old ones did.

 

[Nick Nolte]

Every time someone brings up building their own mobile mesonet the discussion moves towards "why do you need it" or "the data you're collecting is useless, or not research grade." Refer to this thread: http://www.stormtrack.org/forum/showthread.php?20950-Building-a-Mobile-Mesonet for how the conversation typically evolves. Sean Waugh (from above) has done a lot of work with the mobile mesonets on V2, so his knowledge of the subject surpasses most on here and I understand and respect his passion for the design considerations and calibration techniques used in the research environment.

Most of us, however, do this sort of self instrumentation so that we're our own data point out there in the field. Most of us doing this will probably run our gadgets for a day or two and compare it to the nearest ASOS station and if it's the same call it good. There is no harm for one to have their own instrumentation out there (unless it flies off their vehicle), whether they want to stick a Davis on top of their car or design something of their own. While I tend to agree with those saying building one for attention is not a good reason, it's your reason, and that is all that matters.

I'm a bit biased on this subject as I've been constructing my own mesonet for my car, custom electronics and all and it's a learning experience for sure, and I've had a blast building it. I for one am a data junkie, I love having information and data about anything and collecting the data out in the field is no different. To me it just enhances my time out in the field, that's why I'm doing it.

To those who want to stick stuff on their car, go for it.

 

[Sean Waugh]

I am not in any way trying to discourage people from installing stuff on their vehicles. Instrumentation can play a major role in storm chasing if used correctly. It's not all about data collection and V2 level aspirations. As an example, say your chasing a storm with a strong meso that becomes rain wrapped. Visibility is almost zero, your radar image is at least 5 minutes old, and you can't tell where the meso and possible tornado is with respect to your position. A wind vane on top of your car (if installed correctly) would tell you your position relative to the meso. So I fully admit that there are legit reasons to have equipment besides collecting data and initializing a hi-res model with it. I merely wanted to point out that there are significant considerations that should be made before attempting to collect data. Simply purchasing a weather station, whether intended for a vehicle or not, and strapping it to the top of your vehicle is not going to give you the data you might think. Stationary sites have vastly different considerations that need to be made to ensure quality data. Those considerations do not all apply to mobile setups.

This is my basic point. If one doesn't care that much about accuracy that is fine, but be aware that there are errors that can easily be encountered which can significantly alter the data you see, possibly leading to false conclusions.

 

[Nick Nolte]

The trickiest part of a mobile mesonet is probably getting the true wind direction and speed while in motion. In my setup I'm using GPS while the car is moving then some vector math to calculate the speed and direction (you can see a visual explanation of this in the thread I linked in my previous post). However, once you are stopped, GPS is not reliable for heading (or speed for that matter) information. In my setup I've incorporated a tilt-compensated compass (which I still need to test/calibrate) to use for heading when my car is stopped or traveling below a few miles per hour.

I've never owned a Davis station, but I assume there's a readout giving the direction, but that will be relative to where you have "north" positioned on your car and it will only give you a true direction if you're stopped *and* facing north, otherwise it will always be a relative direction. If you have the instrumentation on your car mounted such that north is towards the front of your vehicle, I suppose if you get a westerly reading you will know the wind is coming from your left and can figure out the actual direction in your head, but as Sean mentioned, in a tense situation that kind of on-the-go mental calculations could be lacking in accuracy. Without software compensating for vehicle motion, if you're travelling north at 50mph and there's a westerly wind at 50mph, your station will read a northwesterly wind at 70mph.

Sean, I appreciate your input on this (and past) threads. Are you aware of significant differences in readings in values aside from wind speed/direction? I mean is there a difference in temperature/humidity values 1 foot off your roof (in the slipstream) as opposed to 4 feet above the roof (differing aerodynamic profiles not withstanding) The two effects that come to mind is radiational from your roof itself and perhaps compressional from being in the slipstream?

 

[Sean Waugh]

Sean, I appreciate your input on this (and past) threads. Are you aware of significant differences in readings in values aside from wind speed/direction? I mean is there a difference in temperature/humidity values 1 foot off your roof (in the slipstream) as opposed to 4 feet above the roof (differing aerodynamic profiles not withstanding) The two effects that come to mind is radiational from your roof itself and perhaps compressional from being in the slipstream?

Nick, there are a lot of factors that one must consider when trying to make temperature and RH measurements on a moving platform. Just to list a few of them off: shielding from rain (also known as wet-bulbing), aspiration rate, proximity to vehicle, response time of the sensor, response time of the instrument housing. There are MANY more factors that can influence a measurement of T/RH, but in my opinion these are some of the major ones. The sensor must be housed in something that protects it from, but still allows proper aspiration through the unit. This is important to not only keep the sensor dry, but to make sure that the sensor is being mixed adequately with the local air. Failure to do this would result in very poor readings. Proximity to the roof is always a tricky business. I have seen on multiple vehicles, including those used in VORTEX 2, temperature sensors being influenced by the heat generated by the vehicle. If you have the sensor arrangement too close to the car roof (ie in the slipstream of the car), you run the risk of picking up that heat as it is carried over your vehicle. Compressional heating isn't really an issue, but reflectance and re-radiance from your car roof is a substantial issue. This is going to vary from vehicle to vehicle with not only color but what type of material the car roof is made from. Putting it as far above your car roof as possible is always the best course of action.

And this is just for temperature and RH. Wind speed and direction have their own set of caveats that must be considered. It doesn't matter how accurate your wind anemometer is, if it's placed 3 inches above the car roof it's not going to be accurate. When you are that close to the car you get accelerated airflow over the roof of the vehicle and the wind direction over the vehicle is significantly influenced by the placement on the vehicle and the shape of the vehicle. This is going to complicate things extremely when trying to back out the true wind direction and speed. To get completely out of the slipstream of the car you'd have to go an average of 3x the height of the car (which isn't really feasible), but getting at least 3-4 ft above the car gets you away from most of the effects (again, this will depend on the type of vehicle you're driving).

Tip of the iceberg on this kind of stuff. I could go on for days talking about all the considerations that need to be made. Knowing the limitations of one's setup is probably one of the most important things when dealing with instrumentation.

 

[Nick Nolte]

Sean, thanks again for the response! I hope the others in this thread don't feel we've deviated from the main topic at hand. Dustin may have just been looking for equipment recommendations, but I hope this information proves valuable as well.

TWISTEX had posted a PDF on their facebook page linking to the 1995 mobile mesonet documentation that showed the aspirated weather shield, what was inside, etc...Here it is: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0426(1996)013<0921:AMMFFM>2.0.CO;2 That is what I based my design on as far as the shielding goes.

The rest is a little different since the front is left open for a camera, my wind mast is probably at least 3 feet above my roof. The diagrams in that PDF show their wind instruments just above the windshield, whereas mine is towards the back of my roof, but high enough where the slipstream effect will be minimal...they have a useful diagram in that document showing the air stream over a car.

I recall in that prior thread you mentioned some lag in the response time of the probes inside the "J Tube" as you called it. Is that the same thing in the pictures of the PDF I linked? You had linked a PDF in your post in that thread, but it's broken. Now that I look at the URL it may have been the same document I linked, lol.