According to MetOne (http://www.metone.com)....
The AIO 2 Weather Sensor provides measurements of wind speed, wind
direction, ambient air temperature, relative humidity, and barometric
pressure in a single, compact, rugged unit. It integrates a folded-path,
low-power sonic anemometer with a precision thermistor temperature
sensor, fast-response capacitive relative humidity sensor, and a
state-of-the-art barometric pressure sensor. It also includes an
internal flux-gate compass that allows for automatic alignment of wind
direction to magnetic north, regardless of the sensors orientation.
The small footprint and power efficiency of the AIO 2 make it ideal for
remote regions, urban environments, air quality networks,
construction/remediation sites, and other network applications. The unit
can be used in permanent (cooperative weather networks, schools, public
information dissemination) or temporary (emergency response, audit,
research program support) installations.
Designed for maximum portability and utility, the AIO 2 is well suited
for rapid deployment and use by one person under all conditions. The
unit may be mounted on a tower, tripod or vehicle mast. Data output is a
serial, digital message that can be interfaced to most data logging
The AIO 2 even has the capability to connect an external contact closure
rain gauge (such as the Met One 360 or 370) and/or solar radiation
sensor (such as the Met One 096A-2). If these inputs are present, their
measurements are then integrated into the AIO 2 serial data output.