WALTA Strawman Station

Overview

The WALTA Strawman Station is a precursor to the equipment which would be placed at each site in the WALTA array. The strawman station allows us to make preliminary studies of how we would build the stations.

The strawman station consists of a computer with two temperature sensors and a GPS receiver. A central computer polls the station at regular intervals for information from the sensors. Web pages hosted at the central computer can generate time-series plots of data received from the station.

24-Hour Station Logs

These charts are generated from data stored in the central computer.

• Temperature
• GPS Altitude
• GPS Latitude
• GPS Longitude
• GPS Satellite Tracking
  "Visible" is a GPS term which essentially means "How many satellites would be visible if the antenna had an unobstructed view of the sky?" Or, put another way, "How many satellites are above the horizon?" "Tracked" is the number of satellites actually used by the GPS unit to generate a position fix, and is affected by buildings, trees, and other objects which might obstruct the path between the antenna and the satellite. Our GPS system cannot track more than eight satellites at a time.

Averages

Interesting (or not-so-interesting) averages generated by the logs in the central computer.

• Averages by Station
• Averages by Time of Day

Temperature History

• Noontime Temperatures
• Midnight Temperatures

Direct Station Queries

These queries are handled directly by the station. The results consist of live data. The different formats exist for parsing by different possible programs.

• XML Format

See Document-Type-Definition at the beginning of the XML.

• Basic Information, CSV Format

One line of information. Each field is separated by a comma.

Field	Name	Type	Units
1	Location ID	Integer	n/a
2	Location Name	Text	n/a
3	CPU Time	Unsigned 32-bit integer	seconds since Jan 1, 1970
4	GPS Time	Unsigned 32-bit integer	seconds since Jan 1, 1970
5	GPS Latitude	Float	degrees
6	GPS Longitude	Float	degrees
7	GPS Altitude	Float	meters
8	Internal Temperature	Float	celsius
9	External Temperature	Float	celsius

• GPS Satellite Information, CSV Format

One line per satellite. Fields within each line are separated by commas.

Field	Name	Type	Units
1	Location ID	Integer	n/a
2	CPU Time	Unsigned 32-bit integer	seconds since Jan 1, 1970
3	GPS Time	Unsigned 32-bit integer	seconds since Jan 1, 1970
4	Satellite ID	Integer	n/a
5	Azimuth	Integer	degrees
6	Elevation	Integer	degrees
7	Health	Text	n/a
8	Tracking Status	Text	n/a

• TCL List

One line of information. Each parameter is a name-value pair, enclosed within braces, and separated by white space. For N pieces of information, the line looks like-
{name1 value1} {name2 value2} ... {nameN valueN}

The names of the parameters currently available are id, cpu_time, gps_time, latitude, longitude, altitude, t0, t1, gps_visible, gps_tracked, gps_visSatOverflow, gps_rstatus. The parameters and their order are subject to change.

Possible Projects

Temperature Calibration

The temperature sensors have not been calibrated. They are probably off by a degree or two in absolute scale, and possibly by a few percent on a relative scale. An ice-water bath would help set the absolute calibration.

GPS Satellite Paths

We record the azimuth and elevation of each GPS satellite. This information could be turned into a plot of the path of each satellite across the sky. Blank points should appear in the plot where objects such as trees and buildings obscure the antenna's view of the sky.

GPS Fuzziness

This page includes plots of how much the reported GPS latitude and longitude varies in degrees. How large is this variation in meters? The variation is due to a combination of uncertainty in making a measurement and the military's deliberate altering of the information, known as "selective availability."

Position Survey

Are there any ways to survey the location more accurately than using our GPS readings? With selective availability a factor, what is the best way to average our GPS position measurements together?

Temperature History

Plots from this page show 24-hour temperature histories. What other use can be made of the temperature history? A plot showing the temperatures only at midnight? A comparison of midnight and noon temperatures?