Data

General

The sensors used in FOOTPRINT92 are listed in Table 1 and shown schematically in Figures 5 and 6. Each sensor is associated with a system identification number (sid) that is composed of an ADAM name and channel number (e.g. cosmos 202). Channel numbers from 100 - 199 indicate an analog input channel and channel numbers from 200 - 299 indicate a serial input channel. Each sensor has one, and sometimes more, output variables associated with it.The variable names each have a data identification number (did) used to identify the archived data. (e.g. u.prop.4m and v.prop.4m). All data acquired during the deployment is archived. In addition, the application of the appropriate calibration and delay functions convert this raw data to engineering or scientific units. This processed data is available as 5 minute block averages of the means and covariances obtained from the initial processing of the variables measured. These block averages are termed "covars". The format of the covars is relatively easy to decipher. Thus, the 5 minute mean of the concentration of SF6 measured using the fast response SF6 sensor at the 50 meter flux station sampling at the height of 10 meters is represented as conc.sf6.50.10m and the 5 minute mean of the covariance of the vertical air motion measured by the University of Washington sonic anemometer and the temperature measured by the AIR fast response temperature sensor at the 100 meter flux station at the height of 5 meters is represented as w.100.5m:t.100.5m. At the end of each day the raw data is transferred to an Exabyte magnetic tape. To reduce the risk of data loss the data for each day is stored on a separate tape. The raw data is then erased from the on-line hard disk. All covars and other derived products remain on the disk and are available for the duration of the deployment.

The available statistics variables are presented in the appendix of this report in Table 5. The actual file in NetCDF format are available for download here.

Daily weather plots

A selection of covar plots were produced daily to provide a review of the operations. These are termed "Daily weather plots".

The daily weather plots presented in the appendix of this report are (a) temperature, humidity, pressure and rainfall, (b) wind speed and direction, (c) net radiation, sensible heat flux, latent heat flux, and surface heat flux and (d) z/L, u* and the Bowen ratio. The plotted data are 5 minute covar plots, except for the turbulent flux data, sensible and latent heat fluxes, z/L, u* and the Bowen ratio, which are 20 minute averages.

The daily weather plots are presented in the appendix of this report.

Wind

The prop-vanes are integrated sensors which yield wind speed and direction directly as a serial output. The prop-vane wind components are output in a geographic coordinate system; where u is wind from the west and v is wind from the south. The propvanes are individually calibrated for wind speed response in the SSSF wind tunnel prior to the deployment.

The sonic anemometers are integrated sensors. The ATI sonic anemometers output the three orthogonal wind components and the derived speed of sound temperature. The UW sonic anemometers measure three non-orthogonal wind components from which the three orthogonal wind components are calculated. In both cases, the wind components are in an instrument-oriented coordinate system, where u is the wind along the instrument boom towards the tower and v is the wind from right to left as you face in the positive u direction. A nominal bearing derived from the azimuth of the mounting boom is used to obtain the approximate geographic wind components during the field program. In post project analysis of the sonic anemometer data, the accurate geographic winds are derived by matching the sonic anemometer data with that of the propvanes.

Psychrometry

The psychrometers are integrated sensors which yield relative humidity and temperature directly as output. From these measured values other moisture parameters can be calculated.The psychrometers are calibrated in the SSSF calibration lab prior to the field program

Radiation

The radiation stand bearing the radiation sensors was positioned over a representative surface with grass, small scrub and a patch of sand. The 3-meter-long horizontal beam of this radiation stand was 3 meters above the ground and oriented nominally east-west (a theodolite sighting indicated the bearing to be 260° 48'). The level-adjustable assembly bearing the radiation sensors was mounted on the beam and leveled to within 15'. Six radiation sensors were deployed: a four component radiation array monitoring incoming and outgoing short and long wave radiation with Eppley radiometers, a REBS net radiometer, and an Everest surface temperature sensor. The two long-wave radiometers and the net radiometer output analog voltages. The short-wave radiometers gave similar signals together with thermistor output defining the temperature of the instruments' case and dome. This enabled a correction to be made to compensate for the direct sunlight heating of the dome of the shortwave sensor.

It is important to appreciate that the short-wave radiometers and the net radiometer view a hemisphere with a cosine weighting factor. For the incoming radiation this presents no difficulty if the sensors are horizontally level. For the outgoing radiation it implies that the effective viewing area of the sensors at 3 meters height is only a few tens of square meters. This constraint puts a premium upon the representativeness of the surface under the radiation stand.

The Everest surface temperature sensor has a collimated 30 degree cone and views a patch of the surface less than ten square meters in area. The sensor yields an output directly in degrees centigrade by using an assumed infrared emissivity of 0.95.

Soil parameters

Three locations, corresponding to the three dominant surface covers, sagebrush, senescent grass, and bare sand, were instrumented to determine the surface heat flux. At each location four soil temperature probes were inserted at 1 cm, 3cm, 5 cm, and 7 cm depth, and a soil heat flux plate was buried at 8 cm. The output of the four soil temperature probes were connected to the data system via a self timing multiplexer. The multiplexer generated an indicator signal to enable the correct assignment of the different outputs. The temperature profile of the soil and the average temperature of the top 8 cm was determined. Generally, every day or so, the soil moisture for the top 8 cm of soil was determined near mid-day using the gravimetric, dig, cook and weigh method. Soil samples were taken at the three locations and returned to the laboratory for subsequent analysis. The bulk density, the mineral density and an estimate of volumetric organic fraction were determined for the FOOTPRINT92.

From these parameters and the gravimetric water fraction the volumetric heat capacity of the soil and hence the heat capacity of the top 8 cm of the soil was determined. From the heat capacity and the varying average temperature the heat stored in the layer of soil above the heat flux plates was calculated. The heat flux measured at the 8 cm depth was subjected to the Phillips correction, to compensate for the effect of the different heat conductivities of the heat flux plate and the soil. The soil heat flux at 8 cm depth taken together with the heat stored in the top 8 cm of soil yield the heat flux at the surface of the soil.

Logbook

An electronic logbook was maintained during the field program. A total of ~170 entries were made during the FOOTPRINT92 deployment in 17 different categories: 1 COMMENT, 2 METALOG SUGGESTION, 3 LOG, 4 STATUS, 5 SONIC 6 PSYC, 7 PROP, 8 RAD, 9 FASTT, 10 KRYPTON, 11 SF6, 12 BUGFLUX, 13 CONDSAMP, 14 WEATHER, 15 SOFTWARE, 16 CALIBRATION, 17 OPS.