Instrumented car for mobile turbulence measurements

As a complement to aircraft and tower turbulence measurements, an instrumented surface vehicle can measure atmospheric mean state and turbulence while traversing the surface. Here we describe a system that has been implemented on a car. This system has unique advantages: it is able to measure the horizontal structure in urban canyons, within and at the edges of forests, in cold pools, or along terrain slopes, where other measurement systems are difficult to deploy. It is particularly useful for studies requiring nighttime or near-surface measurements of horizontal atmospheric characteristics at a strictly constant height above the ground, such as in very stable conditions or for estimating horizontal derivatives. The simplicity and low cost of operation enables longer-term deployment compared to aircraft observations.

We present the details of the instrumented car platform and show that it can be used for turbulence measurements. The basic car instrumentation includes a 3D sonic anemometer, and a miniature GPS-INS that is used to measure and remove the car motion for obtaining the true wind vector. The flow correction procedures are similar to those used in aircraft observations, except that the car motions are shown to be much simpler and less variable. As a result, the only crucial corrections and transformations required for obtaining the final wind are: removing the longitudinal car speed, removing the mean vertical speed induced by the flow distortion, and rotating the horizontal wind to the meteorological coordinate system.