Calypso Mini Wind Meter

[SteveLM]

The Calypso Mini Wind Meter ( https://calypsoinstruments.com/shop...sonic-portable-mini-wind-meter-73?category=1# ) is a tiny device that claims to measure wind speed and direction to high accuracy. See the link for all the technical details. At 1.69" in diameter and 1.85" tall, it's amazingly compact. The box also includes an inductive charging pad and a short USB connecting cable. Interestingly, the Calypso is intended to sit on the charging pad upside down. A full charge is said to provide 150 hours of operating life.

The device is based on paired ultrasonic sensors that measure air movement through a gap in the middle of the device. Otherwise, it is nearly completely featureless, with no status LEDs or other readouts to indicate that it is operating. There isn't even an I/O switch! Instead, the Calypso comes with a companion app (Android and iOS) that provides the device status (battery charge) and wind readouts. The app also provides weather information (temperature, pressure, humidity...) via the Internet from a local weather source.

So, how does this ultrasonic technology compare to our familiar Kestrel? Unfortunately, my local weather has been becalmed for the last several days, with only occasional slight whispers of wind. So I decided to set up a simple table top test to get at least a rough comparison between my Calypso and my Kestrel...

As shown, I positioned a table fan so that it blew along the top of a smooth hobby table. Hard to tell, but the fan is positioned so that the table top is centered on the fan face, a crude attempt to get the air flowing parallel to the table surface. The Calypso was placed on a small box to get it away from the table surface (the boundary layer) and the Kestrel was placed so that its sensor was away from the wake of the Calypso (more or less in undisturbed fan air). I tried a couple of fan speeds, but they turned out to be not that different.

The results? The Calypso and the Kestrel generally agreed within about 1.3 mph of each other. Sometimes they were almost exactly the same, but sometimes they differed by up to 2 mph or a little more. This result is likely due to the software damping algorithm that each device uses to smooth out the fluctuations that each sees in wind speed. Also, a table top fan isn't exactly a precision air blower. As I said, this was a rough test.

The photos show two of the four display modes that the user can choose; the second photo is the "ballistic" screen.

Finally, a couple of pros and cons. The Calypso is highly compact, simple and portable. But I think it's more at home in a fixed location than on the move. A big plus is that it provides wind direction much more accurately* without fussing with how it's held as is the case with the Kestrel. However, it doesn't provide weather data exactly at your location (as the Kestrel does) and instead provides Internet "local" data. Also, the Calypso requires at least 1 meter / sec of wind before it starts providing output. Finally, I'm a bit concerned with how long the battery will last. Without an I/O switch, the battery will inevitably run down; if the Calypso is stored away for the season, will the battery charge back up when you need it? I don't know. (I've tried to contact Calypso in Spain about this, but my e-mails keep getting bounced back...)

* I didn't mention it, but I tried rotating the Calypso on the table top and it responded appropriately to the angle change...

 

[SteveLM]

After literally weeks of calm winds, we finally got a breezy day today, so I took the opportunity to test the Calypso outside along with my Kestrel. Using its mounting point, I attached the Calypso to a tripod and extended the legs and mast so that the Calypso was sitting at nearly the same height as my head (so about 6 feet above ground level). I walked out to a spot that was about as far away as I could get from the surrounding trees and houses. I aligned the Calypso so that its reference mark was pointed north and I stood several feet away also facing north.

I fired up the Kestrel and, holding it at the same level as the Calypso, spent about 20 minutes watching the two wind measurements. Winds were gusting up to about 6-8 mph with average wind probably about 1.5 - 2 mph during the time I was outside. No pictures this time (not enough hands) but the Calypso and the Kestrel correlated very well whenever the wind gusted long enough for both instruments to get a steady reading. Wind speeds from both were usually within a small fraction of a mph; I often saw speeds that were only 0.1 mph different. Calypso's wind direction sensing was excellent and when the winds were steady enough (for a second or two) it always correlated with the wind direction against my face (note that when measuring wind speed, I tried to steer the Kestrel in the appropriate wind direction, sometimes using the Calypso as a cue to that direction).

When the winds shifted, the speed measurements diverged, undoubtedly due to the particulars of each instrument's sensing technology. The Calypso's wind direction measurement lagged as well. I don't think that there was anything unexpected about this.

Although this was not a day-long field test, my bottom line is that the Calypso delivers on its promise of accurate wind speed and direction. In the latter case, it is superior to the Kestrel which, of course, relies on you to sense wind direction. In other outdoor test attempts, I've been able to back off 20 to 25 feet before I start seeing Bluetooth connectivity problems, so the Calypso offers reasonable flexibility in locating it to get good wind measurements at a single nearby point. As someone else pointed out, it's not by itself a wind solution, but it certainly is an aid to helping you estimate a wind solution...