ARM/GCIP NESOB-97 30 Minute Skin Temperature Composite 1.0 General Description This 30 minute Skin Temperature Composite is one of several surface-layer data sets provided in the Atmospheric Radiation Measurement(ARM)/Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) Near Surface Observation Data Set - 1997 (NESOB-97). This Skin Temperature composite was formed from three data sources: the 10m and 25m ARM/Clouds and Radiation Testbed (CART) Multi-Filter Radiometer (MFR) 20 second data, and 30 minute data from the GCIP National Oceanic and Atmospheric Administration (NOAA)/Atmospheric Turbulence and Diffusion Division (ATDD) Little Washita, Oklahoma long term flux monitoring site. This composite was developed by the merging of the 30-minute averaged values of skin temperature as provided by NOAA ATDD for its Little Washita station and the 30-minute averaged values of skin temperature as derived by University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) from the 20-second values provided by ARM for its 10m and 25m MFR stations. UCAR/JOSS computed standard deviations for the ARM 10m and 25m MFR data when at least 15 observations were available within the 30-minute averaging interval. JOSS did not do any other quality control on the data set. This composite contains data for the ARM/GCIP NESOB-97 domain and time period (01 April 1997 through 31 March 1998). The ARM/GCIP NESOB-97 domain is approximately 100.5W to 94.5W longitude and 34N to 39N latitude. 2.0 Detailed Data Description The NESOB-97 Skin Temperature Composite is composed of data from three sources which report data at different frequencies. 2.0.1 ARM/MFR Algorithms The Multi-Filter Radiometer (MFR) is used for skin temperature measurements. It is simply a sensing head from the Multi-Filter Rotating Shadowband Radiometer (MFRSR) that is turned upside-down and points at the ground. It measures upwelling spectral irradiances (with units W/m^2/nm) at six different wavelengths. There's also a broadband detector that uses a silicon photodiode to measure the broadband radiation. Because the response of the photodiode does not capture the entire broadband spectrum this detector is uncalibrated and the measurements from it are reported in counts. The six filter detectors measure the spectral irradiances at nominal wavelengths of 415, 500, 610, 665, 860, and 940 nm. These measurements are made over a spectral range of about 10 nm. The full width at half-maximum of the interference filter passband is about 10nm. The accuracy of the spectral measurements is about plus or minus 4% if the interference filters do not drift. For the NESOB-97 time period, the MFRs were equipped with filters that did drift, and this drift was significant. So it's possible that some of the spectral measurements could be off by as much as 50%. Errors this large are probably confined to the 610 and 665 nm wavelengths; for other wavelengths the error is probably much smaller. Exactly what those errors are is not known, because there's no way to monitor the calibration stability of this instrument while it is deployed in the field. Standard deviation is reported for the skin temperature parameter when a minimum of 15 observations are reported in the 30 minute time period. The algorithms used by ARM to produce the raw MFR skin temperature data are not currently available. 2.0.2 NOAA/ATDD Algorithm Standard meteorological sensors are sampled every 2 seconds with a datalogger and multiplexor (CR21x, Campbell Scientific, Inc.) and averages are computed every 30 minutes, coincident with eddy covariance data. No standard deviations were calculated for the Little Washita data, since it originated in 30 minute frequency. The algorithms used by NOAA/ATDD to produce the Little Washita skin temperature data are not currently available. 2.1 Detailed Format Description The ARM/GCIP NESOB-97 Skin Temperature Composite contains 8 metadata parameters and 3 data parameters. The metadata parameters describe the date/time, network, station, and location at which the data were collected. The 3 data parameters repeat once for each 30 minute period from UTC 0000 through UTC 2330. Data reported for a designated 30 minute time represents data collected during the previous 30 minute period. All times are reported in UTC, and skin temp values are reported in degrees Celsius. Each data value is followed by a Quality Control flag, but UCAR/JOSS does not Quality Control the data at the present time. The Quality Control flag is set to "U" for "Unchecked", unless the datum is missing, in which case the flag is set to "M". The table below details each parameter in the composite data set. Parameters Units ---------------------- ----------------------------------- Date of Observation UTC Time of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network dependent Latitude Decimal degrees, South is negative Longitude Decimal degrees, West is negative Station Occurrence Unitless Station Elevation Meters above sea level Skin Temperature Celsius QC flag U or M Standard Deviation Celsius 2.2 Data Remarks Missing values are -999.99. The standard deviation was calculated for the ARM 10m and 25m MFR Skin Temperature values when there were at least 15 measurements in the 30 minute averaging interval. No standard deviations were calculated for the Little Washita data, since it originated in 30 minute frequency. 3.0 Quality Control Processing This data set was not Quality Controlled by the Joint Office of Science Support (UCAR/JOSS). 4.0 References Barnard, Jim, 1999, e-mail communication Meyers, Tilden, 1999, NOAA/ATDD Little Washita Watershed Long Term Flux Site, information supplied with data Multi-Filter Rotating Shadowband Radiometer (MFRSR), http://www.arm.gov/docs/instruments/static/mfrsr.html (data for filter characteristics reflect filters installed since NESOB-97)