Temperature Verification
The daily maximum and minimum temperatures from the AWS are routinely compared to a digital max/min check thermometer and also to official stations in the nearby BoM AWS Network. This page outlines our methods of comparison and presents the ongoing results.
Check Gauge Comparison
The AWS thermo-hygrograph is housed in a solar powered fan aspirated radiation shield (FARS) that protects it from direct solar radiation and other sources of radiated heat. The digital max/min check thermometer is housed in a standard BoM Stevenson Screen and is classed as the reference thermometer for this comparison stage. From past experience our Stevenson Screen is known to exhibit a significant time lag when there is a sudden temperature change: the passage of a cold front will not be evident in the temperature trace for many minutes, whilst brief temperature peaks due to breaks in the cloud cover will usually be missed.
Despite the time lag shown by Stevenson Screen, a daily comparison is made by subtracting the temperature recorded by the AWS from the temperature recorded by the check thermometer. The daily results are collated and presented in the following table under the heading Mean Check Bias. If the mean check bias is positive the check thermometer has a warm bias and is warmer than the AWS, and conversely if the mean check bias is negative the check thermometer has a cool bias and is cooler than the AWS.
The aim of this comparison stage is to achieve a negligible bias, indicating a very good agreement between the sensors under the same ambient conditions. This is the most reliable measure of the accuracy of the AWS maximum and temperature temperature data.
Buddy Comparison
The nearby BoM AWS Network consists of stations at Laverton RAAF, Avalon Airport, Point Cook RAAF, Melbourne Airport and Essendon Airport. The temperature sensors used in these AWS are highly accurate platinum resistance thermometers. They are housed in standard BoM Stevenson Screens and located in well maintained open areas with good all around exposure in accordance with BoM specifications.
Melbourne Airport and Essendon Airport are both considered unsuitable as a buddy for geographical reasons. Laverton RAAF, Avalon Airport and Point Cook RAAF are geographically similar to Truganina and are all deemed to be suitable as a buddy. The temperatures from these three stations often vary considerably under similar conditions, meaning no single station is a perfect buddy. The methodology adopted for this comparison stage is a three station buddy system.
For both maximum and minimum temperature, the highest and lowest comparison temperatures each day form a temperature range to which a nominal 0.5° C buffer is applied to create a daily buddy range. This conservative adjustment allows for the natural variability of temperature and the effects of siting meteorological instrumentation in an urban environment.
A daily comparison is made by testing if the temperature recorded by the AWS is within the buddy range. The daily results are collated and presented in the following table under the headings Within Buddy Range and Outside Buddy Range.
The aim of this comparison stage is to achieve a majority of the AWS temperatures within the buddy range, indicating a high level of consistency with the nearby BoM AWS. For those temperatures outside the buddy range the aim is to have a small difference.
Comparison Results
This comparison graphic is updated periodically.
The maximum temperature verification shows a negligible bias between the AWS and the check thermometer, plus a high proportion of temperatures within the buddy range. This implies the AWS data are accurate for this location and generally compare favourably with the nearby BoM AWS. The minimum temperature verification shows a moderate warm bias between the AWS and the check thermometer, plus a very high proportion of temperatures within the buddy range. Since the AWS minimum temperature data generally compare favourably with the nearby BoM AWS and the maximum temperature has a negligible bias, the results suggest the warm minimum temperature bias is due to localised warming of the check thermometer in the Stevenson Screen.