Meteorological Instrument Performance Characteristics

General Characteristics of Measurements » Homogeneity » Considerations

Representativeness requires an appropriate match between the scale of the phenomenon being studied and the spatial and temporal coverage of the sensor. It also requires collecting a sufficient and appropriately distributed number of measurements covering that scale. For example, a regularly spaced set of measurements over one minute, where the wind speed is about 10 m/s, is representative of an upstream fetch of 600 meters.

The number and spacing of sensors and the sampling frequency required to give representativeness depends on the scale of the phenomenon being studied. An example of a measurand having particularly high temporal and spatial variability is rainfall.

screenshot of CoCoRAHs precipitation map showing variability in precipitation measurements

Screenshot of CoCoRAHs precipitation map showing variability in precipitation measurements. The level of rainfall uncertainty is highly dependent on density and distribution of rain gauge stations over a region. Mishra, A. K. (2013) found that over Bangladesh, as gauge spacing increases from 5 km to 40 km, correlation coefficients decrease from 82% to 21% while root mean square error (RMSE) increases from 8.29 mm to 51.27 mm. Rainfall measurements at a single gauge also require considering the type of precipitation (e.g., frontal precipitation versus isolated showers), its intensity and duration, the effect of topography, and gauge exposure (i.e., height, whether or not shielded, and surrounding obstructions). Satellite-based rainfall measurements are critical to filling in the inter-gauge gap, but their algorithms have uncertainties due to the use of gauges for ground-truthing. Image from Creative Commons CoCoRaHS

Images from the Plains Elevated Convection At Night (PECAN) project (Geerts et al.) showing the mobile mesonet.

Sensors mounted aboard vehicles allow collection of atmospheric data via mobile instrument platforms. Image from R. Clark.

In terms of representativeness, field research presents particular challenges. For example, consider the deployment of mobile instrument platforms needed to characterize the mesoscale features studied during the Plains Elevated Convection At Night (PECAN) campaign. In this study, an array of fixed and mobiles sites, some with single instruments and others with an assortment of instruments, were used to establish a representative footprint (shown in the map) covering features of interest to the project.

Images from the Plains Elevated Convection At Night (PECAN) project (Geerts et al.) showing the PECAN domain.

The domain from the Plains Elevated Convection At Night (PECAN) project (Geerts et al.) Image from NCAR.

Images from the Plains Elevated Convection At Night (PECAN) project (Geerts et al.) showing a panorama of the observing platforms using in PECAN

A panorama of the observing platforms used in PECAN. Photo courtesy of R. Clark.

Question

What factors need to be considered to determine representativeness?

All of the above must be considered to determine site representativeness.

Please make a selection.