PWS KCAPALOA15, Palo Alto, California, USA

This Personal Weather Station is an Orion LX from Columbia Weather Systems (CWS). It is located on Waverley Street between Santa Rita and Seale, in 94301.

The primary sensor transmitter is a WXT520 manufactured by Vaisala in Finland. It is controlled by a Weather MicroServer from CWS.

The webcam is a Toshiba IK-WB15 all-weather IP camera, looking south, about 10 feet above ground level. It switches to black and white imaging when the light level is low.

The solar radiation sensor (not part of the Orion unit) is an Apogee Instruments model SP-110, whose spectral response is shown here.

Network connection: WeatherBaga 2.3 software runs on a nearby FreeBSD server. It retrieves live data from the Weather MicroServer and from the webcam, formats that data to meet Weather Underground requirements, and feeds it to the Weather Underground collector.

Installation details: The Orion sensor head is 34.4 feet above ground level, which is in turn 26.2 feet above sea level. It is mounted 93 feet from Waverley Street, and 9 feet above the roof surface underneath it, which is painted white. It was installed according to the urban locations guidelines originally written by Davis Instruments.

Notes: The Orion measures wind speed by sending ultrasonic pulses between its vertical prongs several times per second. If the air is moving, those pulses arrive early or late depending on the wind speed and direction. This technique measures instantaneous air velocity. That velocity must be averaged to get a "wind speed", but it can be used in its raw form to determine wind gusts. Since there is no rotating mechanical anemometer, there is no inertia, and the measurements can vary widely from second to second as the wind changes.

The Orion measures rain and hail by analyzing the force of impact of the droplets on its top surface. It can tell rain from hail because their impact is not the same. Your ears know that; the sound of hail on the top of a car is very different from the sound of rain. Here is the manufacturer's brochure about how the technology works.

The Orion measures everything else using capacitative sensors. A few more details about the measurement technology can be found in this brochure on the Vaisala website.

There is a 120-foot redwood tree on a neighbor's property that casts a shadow on the solar radiation sensor for about 20 minutes in late morning.

This page was last updated on 23 August 2011.