Last Modified: 8/17/99 DESCRIPTION OF SURFRAD DATA FILES FILENAME INFORMATION: The files in this directory contain raw daily data from the established SURFRAD station at Table Mountain, and are written in ASCII. The file naming convention is sssjjjyy.dat, where sss is a three-letter station identifier, yy represents the last two digits of the year (i.e., 95 for 1995), and jjj is the Julian day. "tmt" is the station identifier for Table Mountain, Colorado The extension ".dat" is used because both radiation and meteorological data are included. The file "tmt26697.dat" contains all of the radiation and meteorological data for Table Mountain on day 266 of 1997. DATA STRUCTURE: The data files are written in ASCII and are RAW DATA. Calibration factors and/or conversion factors are given below. Processed data that has been through the first level of quality control and assurance and where the calibration factor has been applied can be found at the SURFRAD web site at http://www.srrb.noaa.gov. The files read the following data in this order: lognum, year,jday,ihhmm,dpsp_v spsp_v,upsp_v,xnip_v,dpir_v,dpirc_r, dpird_r,spir_v,spirc_r,spird_r, upir_v,upirc_r,upird_r, uvb_v,uvb_r,par_v,temp,rh,pres, std_dpsp_v,std_spsp_v,std_upsp_v,std_nip_v, std_dpir_v,std_dpirc_r,std_dpird_r, std_spir_v,std_spirc_r,std_spird_r, std_upir_v,std_upirc_r,std_upird_r, std_uvb_v,std_uvb_r,std_par_v, std_temp,std_rh,std_pres,ws,wd, std_wd Data are reported as 3-minute averages of one second samples. Reported times are the end times of the 3-min. averaging periods, i.e., the data given for 0000 UTC are averaged over the period from 2357 (of the previous UTC day) to 0000. The variables, their data type, and description are given below: lognum Campbell prgram line # (ignore) year year, i.e., 1995 jday Julian day (1 through 365 [or 366]) ihhmm hour of the day (0-23), minute of the hour (0-59) dpsp_v downwelling global solar (mV) spsp_v diffuse global solar (mV) upsp_v upwelling global solar (mV) xnip_v direct solar from normal incidence pyrheliometer (mV) dpir_v downwelling thermal infrared (mV) dpirc_r downwelling thermal infrared resistance of case (Kohms) dpird_r downwelling thermal infrared resistance of dome (Kohms) spir_v shaded thermal infrared (mV) spirc_r shaded thermal infrared resistance of case (Kohms) spird_r shaded thermal infrared resistance of dome (Kohms) upir_v upwelling thermal infrared (mV) upirc_r upwelling thermal infrared resistance of case (Kohms) upird_r upwelling thermal infrared resistance of dome (Kohms) uvb_v UVB (mV) uvb_r UVB Resistance (Kohms) par_v photosynthetically active radiation (mV) temp 10-meter air temperature (C) rh relative humidity (%) pres station pressure (mb) ws wind speed (ms^-1) wd wind direction (degrees, clockwise from north) The variables with the std prefix are the standard deviation of the 3-min average of 1-sec data for the given measurement, (i.e std_dpsp_v(i) is the standard deviation of the 3-min average of 1-sec direct global solar in volts). CALIBRATION FACTORS: 1. The Yankee UVB Photometer The UVB Photometer has a response function that approximates the Diffey action spectrum. The calibration factors reported from Yankee Environmental Systems is reported below as a function of zenith angle to convert from Voltage to W/m^2. As soon as the SRRB's CUCF becomes operational, CUCF will provide annual Diffey calibration factors for these instruments as a function of solar zenith angle and ozone and instrument response- weighted calibration factors. Solar Diffey zenith calibration angle coefficient (W m^-2 / V) 21.8 0.144 25.0 0.143 30.0 0.141 35.0 0.139 40.0 0.138 45.0 0.136 50.0 0.136 55.0 0.137 60.0 0.140 65.0 0.145 70.0 0.145 2. The LI-COR Quantum (PAR) Sensor The LI-COR Quantum (Photosynthetically Active Radiation or PAR) sensor measures radiation in the band from 400 to 700 nm, which is the part of the solar spectrum that activates photosynthesis in plants. The PAR sits on the main platform at SURFRAD stations and collects downwelling global radiation in the photosynthetically active band. serial# cal# PSP LICOR #Q22666 -300.99 micromoles s^-1 m^-2/mV (9/3/96) * The procedure to convert umoles (of photons) m^-2 s^-1 to Wm^-2 for various light sources (including the sun) is described in Proceedings of the NATO Advanced Study Institute on Advanced Agricultural Instrumentation, 1984. W. G. Gensler (ed.), Martinus Nijnoff Publishers, Dordrect, The Netherlands. To convert to W/m^2 for sunlight use the conversion factor 4.6 umole/(s*m^2) = 1 W/m^2 3. The Normal Incidence Pryheliometer (NIP) The NIP measures direct solar radiation in the broadband spectral range from 280 to 3000 nm. Those used at SURFRAD stations are calibrated nominally on a yearly basis at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. serial# cal# NIP Epply #30399 8.296e-6 V/Wm^-2 (NREL 9/5/96) * 4. Precision Spectral Pyranometer (PSP) Two PSPs measure downwelling and upwelling global solar irradiance at SURFRAD stations. These instruments are sensitive to the same broadband spectral range as the NIP, 280 to 3000 nm. They are also calibrated nominally on a yearly basis at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. serial# cal# Platform PSP (downwelling) Spectrosun #73-88 9.280e-6 V/Wm^-2 (NREL 6/6/97) * Tower PSP (upwelling) Spectrosun #73-82 8.419e-6 V/Wm^-2 (NREL 6/6/97) * 5. Precision Infrared Radiometer (PIR) Two PIRs measure upwelling and downwelling thermal infrared irradiance. They are sensitive to the spectral range from 3000 to 50,000 nm. For calibration of the PIRs, SRRB maintains three standard instruments, the calibrations of which are traceable to standards at Eppley Laboratory and the World Radiation Center in Davos, Switzerland. serial# thermopile(C1) dome corr (C2) Platform PIR Eppley #31609F3 3.77* 2.24 (SRRB 8/13/97) * Tower PIR Eppley #31608F3 3.98* 2.56 (SRRB 8/13/97) * * units on cal #C1 for PIRs are E-6 V/(W/m^2), #C2 no units. Irradiance is calculated as follows: i) Given: Thermopile Voltage V (mV) Case Resistance Rc (ohm) Dome Resistance Rd (ohm) Calibration Coefficient C1 (V/(W/m^2)) Dome Correction Coefficient C2 (no units) Stephan-Boltzman Constant sigma=5.67x10-8(W/(m2K4)) ii) Calculate: Case Temperature Tc (K) Dome Temperature Td (K) Tc,d = 1E5/(273.09 + 26.3198*L + 0.278237*L^2 + 0.0196739*L^3) where L = ln(Rc,d/1000) and Rc,d is in ohms. iii) Calculate: Irradiance I (W/m2) I(W/m^2) = V/(1000*C1) + sigma*Tc^4 + C2*sigma*(Tc^4 - Td^4) where V is in (mV) Tc,d is in (K) C1 is in (V/(W/m^2)) sigma is in (W/(m^2K^4)). 6. Misc. meteorological parameters: serial# cal# Temp and RH Vaisala #R2410094 Barometer Vaisala #P173002