BOREAS RSS-14 Level-3 Gridded Radiometer and Satellite Surface Radiation Images Summary The BOREAS RSS-14 team collected and processed GOES-7 and -8 images of the BOREAS region as part of their effort to characterize the incoming, reflected and emitted radiation at regional scales. This data set contains surface radiation parameters, such as net radiation and net solar radiation, that have been interpolated from GOES-7 images and AMS data onto the standard BOREAS mapping grid at a resolution of 5 km N-S and E-W. While some parameters are taken directly from the AMS data set, others have been corrected according to calibrations carried out during the second 1994 IFC-2. The corrected values, as well as the uncorrected values are included. For example, two values of net radiation are provided: an uncorrected value (Rn), and a value that has been corrected according to the calibrations (Rn-COR). The data are provided in binary image format data files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS RSS-14 Level-3 Gridded Radiometer and Satellite Surface Radiation Images 1.2 Data Set Introduction A gridded data set of various surface radiation parameters covering a large portion of the BOReal Ecosystem-Atmosphere Study (BOREAS) study area has been produced. Because surface net radiation is generally a main determinant of how the hydrometeorological system operates and how the phenology of a canopy functions, it is a fundamental quantity observed during BOREAS. The project that produced this data set was designed to ensure the highest possible accuracy and precision of the net radiation measurements taken throughout and between the BOREAS measurement sites. This project attempted to assess how well current geosynchronous satellite algorithms, based on two-channel Geosynchronous Operational Environmental Satellite (GOES)-7 visible radiance inputs, can help retrieve surface net radiation at a hierarchy of space and time scales (Hodges and Smith, 1997). All net radiation measurements incorporated in this objective analysis from the multiple sites have been intercalibrated to an Eppley four-way directional pyranometer/pyrgeometer system, for which the calibrations are traceable to the primary radiometer standard maintained at the Davos, Switzerland World Radiation Centre, which is calibrated on the World Radiometric Reference (WRR) scale. The radiometers used in the field were cross calibrated at a common site prior to the onset of the 1994 BOREAS summer field phase. All operational flux stations that used a net pyrradiometer in and between the Northern Study Area (NSA) and Southern Study Area (SSA) were visited for at least one complete solar cycle during the second Intensive Field Campaign (IFC- 2) with one of three transfer net pyrradiometers to check on residual sensitivity differences. The transfer net pyrradiometers had been calibrated against the Eppley four-way system, and thus their role was to transfer the calibration of the Eppley system to the operational net pyrradiometers at each of the BOREAS flux measurement sites. While net radiation was the primary focus of the field phase as well as the post-field analysis, additional surface radiation parameters are also included in the data set. 1.3 Objective/Purpose The primary objective of the field phase was to calibrate all the BOREAS operational net pyrradiometers to a single standard, which itself had been carefully calibrated, and to examine the spatial and temporal distribution of net radiation at different scales. Previous experiments of varying scales have measured net radiation at multiple locations over an extended domain for surface energy balance research. Few of these have actually used net radiation data gathered at multiple sites to examine the spatial and temporal distribution of Rn, and none have systematically addressed the nature of the underlying measurement biases obtained from different models of net radiation measuring devices. It had always been understood in these experiments that a certain degree of error permeated the Rn data sets, but follow up reporting of such data sets has mostly considered intercalibration errors in anecdotal fashion, if at all. It is the intent of this study to focus on these differences and to assess distortions in the space-time net radiation field. This data set is an expanded version of the one used for the net radiation analysis (Hodges and Smith, 1997). 1.4 Summary of Parameters and Variables Thirty-minute averages of surface radiation parameters have been interpolated onto the standard BOREAS mapping grid at a 5 km resolution (the grid covers both the NSA and SSA as well as the transect between the two). This is a continuous data set starting on 16-May-1994 and ending 20-September- 1994 (Julian days 136 to 263). The following surface radiation parameters are included: • Scaled Uncorrected Net Surface Radiation • Scaled Corrected Net Surface Radiation • Scaled Shortwave down at surface • Scaled Shortwave up at surface • Scaled Net Shortwave at surface • Scaled Uncorrected Longwave down at surface • Scaled Corrected Longwave down at surface • Scaled Uncorrected Longwave up at surface • Scaled Uncorrected Net Longwave at surface • Scaled Corrected Net Longwave at surface • Scaled Uncorrected Combined Net Radiation at surface • Scaled Corrected Combined Net Radiation at surface • Scaled Optimal Net Radiation 1.5 Discussion During 1994's IFC-2, Remote Sensing Science (RSS)-14 team leapfrogged three calibrated (calibrated to an Eppley four-way pyranometer-pyrgeometer system) pyrradiometers among all Automatic Meteorological Station (AMS) sites, calibrating the operational net pyrradiometer at each. (Note that this was also done at all the Tower Flux (TF) sites, but those calibrations, or TF data, are not part of this data set. See Hodges and Smith (1997) for more details on TF calibrations.) The AMS net radiation data were then corrected according to the site-specific calibrations. Additionally, the parameters net longwave radiation (L*) and downwelling longwave radiation (L_down) were extracted from the measurements of net radiation (Rn). When Rn was used to extract another parameter, both uncorrected and corrected values of Rn were used, which gave both an uncorrected and corrected value of the extracted variable. All the extracted parameters, along with those parameters that were directly measured (such as downwelling and reflected solar values), were then interpolated onto a grid to produce the data set. 1.6 Related Data Sets BOREAS AFM-07 SRC Surface Meteorological Data BOREAS RSS-14 Level-1 GOES-7 Visible, IR and Water-vapor Channel Images BOREAS RSS-14 Level-1a GOES-7 Visible, IR, and Water-vapor Images BOREAS RSS-14 Version 1 Level-2 GOES-7 Shortwave Radiation Images BOREAS RSS-14 Level-1 GOES-8 Visible, IR and Water-vapor Channel Images BOREAS RSS-14 Level-1a GOES-8 Visible, IR, and Water-vapor Images 2. Investigator(s) 2.1 Investigator(s) Name and Title Dr. Eric A. Smith, Professor 2.2 Title of Investigation Quality Assurance of BOREAS Net Radiation Measurements 2.3 Contact Information Contact 1 -------------------------- Gary B. Hodges NOAA/ERL/ARL/SRRB Boulder CO (303) 497-6460 (303) 497-6546 (fax) hodges@srrb.noaa.gov Contact 2 -------------------------- Dr. Eric A. Smith, Professor Department of Meteorology Florida State University Tallahassee FL (850) 644-4253 (850) 644-9639 (fax) esmith@metsat.met.fsu.edu Contact 3 ------------- Jaime Nickeson Raytheon STX NASA Goddard Space Flight Center Greenbelt, MD 301-286-3373 301-286-0239 (fax) jaime.nickeson@.gsfc.nasa.gov 3. Theory of Measurements Because surface net radiation is generally a main determinant of how the hydrometeorological system operates and how the phenology of a canopy functions, it is a fundamental quantity observed during BOREAS. This project is designed to ensure the highest possible accuracy and precision of the net radiation measurements taken throughout and between the BOREAS measurement sites. This project attempts to assess how well current geosynchronous satellite algorithms, based on two-channel GOES visible radiance inputs, can help retrieve surface net radiation at a hierarchy of space and time scales. All net radiation measurements incorporated in the objective analysis from the multiple sites were intercalibrated to an Eppley four-way directional pyranometer/pyrgeometer system, for which the calibrations would be traceable to the primary radiometer standard maintained at the Davos, Switzerland, World Radiation Centre, which is calibrated on the WRR scale. All radiometers used in the field were cross calibrated at a common site prior to the onset of the 1994 BOREAS summer field phase. All net radiometer stations at and between the NSA and SSA were visited for at least one complete solar cycle during IFC-2 with one of three transfer net pyrradiometers to check on residual sensitivity differences. The transfer net pyrradiometers had been calibrated against the Eppley four-way system, and thus their role was to transfer the calibration of the Eppley system to the operational net pyrradiometers at each of the BOREAS flux measurement sites. In short, gridded fields of net radiation (both corrected according to the site- specific calibrations and uncorrected) have been produced over a large-scale area encompassing the NSA, the SSA, and the transect between the two. Additionally, satellite-retrieved surface net shortwave radiation data were combined with surface net longwave radiation data extracted from the corrected and uncorrected net radiation measurements to produce satellite-based fields of net radiation. Finally, parameters from the AMS sites, including downwelling and reflected shortwave radiation and net longwave radiation, are also included. 4. Equipment 4.1 Sensor/Instrument Description 4.1.1 Collection Environment For the calibrations, the goal was to collect at least one cloud free solar cycle at each site, but because of time and travel constraints, this was not always possible. It is generally considered that very clear skies are required to produce the best calibrations, and while there is certainly some truth to that, in practice, it was found in this case that calibration differences between clear and cloudy skies were very small. All measurements were made outdoors in ambient weather conditions during July and August of 1994. 4.1.2 Source/Platform As mentioned in section 4.1.1, the instruments were usually mounted on a tower, either a walk-up or climber, above the tree canopy. At two field/meadow and two fen sites, the instruments were mounted much closer to the ground. Care was taken to mount the transfer net pyrradiometers in very close to the operational instruments. 4.1.3 Source/Platform Mission Objectives The objective of the main BOREAS TM and AMS towers was to provide a stable fixed location on which to mount various instruments for monitoring fluxes and meteorological conditions, respectively, at the BOREAS sites and across the BOREAS region. 4.1.4 Key Variables The only variable actually measured by RSS-14 was net radiation; however, RSS-14 net radiation is not what is included in the data set. The BOREAS operational net pyrradiometers were only calibrated by RSS-14. This data set includes, among other variables, corrected net radiation according to those correction factors found during the calibrations. The following is a list of the variables included in this data set (all are direct AMS measurements, corrected AMS measurements, or extracted from AMS measurements): 1. Uncorrected Total Net (Rn) 2. Corrected Total Net (Rn-COR ) 3. Solar Down (Kdn ) 4. Solar Up (Kup ) 5. Solar Net (K*) 6. Uncorrected Infrared Down (Ldn ) 7. Corrected Infrared Down (Ldn-COR) 8. Infrared Up (Lup ) 9. Uncorrected Infrared Net (L*) 10. Corrected Infrared Net (L*-COR ) 11. Uncorrected Total Net (L*+ GOES-derived K*) from Merged Products 12. Corrected Total Net (L*-COR+GOES-derived K*) from Merged Products 13. Optimal Total Net from Parameters 2 & 12 4.1.5 Principles of Operation All the radiometers incorporate a thermopile design to estimate irradiance intensities. Basically, the output of the thermopile is proportional to the intensity, so that the output voltage can be multiplied by a constant (a sensitivity coefficient) to give an irradiance value. 4.1.6 Sensor/Instrument Measurement Geometry Net pyrradiometers, for obvious reasons, require as unobstructed a view as possible both above and below the instrument. This is "as possible" because the instrument has to be mounted on something, which invariably obstructs the view to some extent. For upfacing pyranometers (or pyrgeometers), it is easily possible to mount them such that there are no obstructions above the plane of the instrument. These same instruments mounted in a downfacing position have similar view problems/issues as the net pyrradiometer. Pyranometers and pyrgeometers have a 180-degree field of view, while a net pyrradiometer has a 360-degree field of view (180 x 2). 4.1.7 Manufacturer of Sensor/Instrument Q*6 Net Pyrradiometer Radiation and Energy Balance Systems, Inc. P.O. Box 15512 Seattle, WA 98115-0512 (206) 624-7221 (fax) (206) 228-4067 ------------------------------ Eppley Instruments (PSP, PIR, Everest 4000) The Eppley Laboratory, Inc. 12 Sheffield Avenue P.O. Box 419 Newport, RI 02840 (401) 847-1020 (fax) (401) 847-1031 4.2 Calibration Three new net pyrradiometers were purchased for this study, known as the "transfer radiometers." These three instruments were calibrated against a four-way pyranometer/pyrgeometer system. One pyranometer and one pyrgeometer were sent to The Eppley Labs for calibration. The other pyranometer and pyrgeometer were then calibrated against the first two. 4.2.1 Specifications • Eppley Labs Precision Spectral Pyranometer model PSP • Eppley Labs Precision Infrared Radiometer model PIR • Eppley Labs Infrared Thermometer (IRT), Everest model 4000 • Radiation and Energy Balance Systems (REBS), Inc., Net Pyrradiometer model Q*6 The Eppley PSP measures shortwave radiation in the spectral sensitivity range of 0.285 to 2.8 microns, and the Eppley PIR measures longwave, or terrestrial, radiation in the spectral range of 3.5 to 50 microns. Both the PSP and the PIR can be mounted in either an upfacing or a downfacing position to measure downwelling or upwelling fluxes. The Everest model 4000 measures the surface temperature, which can then be converted to irradiance by the Stefan-Boltzmann law. The Q*6 measures net radiation in the spectral range of 0.25 to 60 microns. Note: RSS-14 used three Q*6 instruments to calibrate the operational instruments. The Q*6's were calibrated prior to and after being in the field with a four-way system consisting of two PIR/PSP pairs. The data contained in this data set were ALL collected with the above types of instruments located at the AMS sites, NOT with RSS-14 instruments. The RSS-14 net pyrradiometers were used solely for calibration purposes. The calibration process and results are discussed in detail in Hodges and Smith (1997). 4.2.1.1 Tolerance It is not possible to state what the accuracy of the measurements are, i.e. how accurate the between-site gradients of net radiation are. In the end, the final accuracy will likely be determined by modelers who are using these data between sites. Instrument sensitivity: REBS Q*6 Sensitivity is listed as 0.0775 mV/(W m-2) Eppley PSP Sensitivity is listed as 0.0009 mV/(W m-2) Eppley PIR Sensitivity is listed as 0.0004 mV/(W m-2) 4.2.2 Frequency of Calibration Pre- and post-field calibrations were performed on the instruments RSS-14 took into the field. These calibrations were approximately 5 months apart. 4.2.3 Other Calibration Information The instruments used were not modified in any way. 5. Data Acquisition Methods Data were collected in situ. At each of the 10 AMS sites, one net pyrradiometer was operated. The calibrated net pyrradiometer (see Section 3) was run alongside each operational net pyrradiometer. Most of the instruments were located above the canopy on a tower, but a few sites were in fields or fens where the instrument was located close to the ground. The BOREAS Experiment Plan provides good descriptions of the characteristics of each site. For the calibrations, the goal was to collect at least one cloud-free solar cycle at each site, but because of time and travel constraints, this was not always possible. It is generally considered that very clear skies are required to produce the best calibrations, and while there is certainly some truth to that, in practice, it was found in this case that calibration differences between clear and cloudy skies were very small. RSS-14 used Campbell Scientific 21X data loggers to record the net radiation measured. The transfer net pyrradiometers were colocated with the operational instruments. 6. Observations 6.1 Data Notes The goal was to measure at least one complete cloud-free solar cycle at each site. This goal was not attainable at every site. An analysis of cloudy skies on calibration was performed, and it was found that for this calibration approach, clouds had a negligible effect. Efforts to use only the most cloud- free periods from each site were made nonetheless. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage A parallelogram comprises the extent of the spatial coverage. This area was chosen such that no portion of the parallelogram extended very far outside the domain of the AMS network. (To include the northwest portion of the NSA, it was necessary to extend the parallelogram beyond the AMS network’s domain). The spatial coverage of this data set is a parallelogram with the corners: Latitude Longitude BOREAS X BOREAS Y -> NW 56.57772°N 101.60420°W 575 660 -> NE 55.96247°N 95.47948°W 960 660 -> SW 53.43708°N 108.13830°W 190 275 -> SE 53.15204°N 102.37890°W 575 275 7.1.2 Spatial Coverage Map The following figure shows the boundaries of the BOREAS region and the area used for this analysis. See the companion .gif file (domain.gif). 7.1.3 Spatial Resolution The spatial resolution of the gridded data is 5 km E-W and 5 km N-S. The spatial resolution for the GOES imagery is nominally 1 km. 7.1.4 Projection The area mapped is projected in the BOREAS Grid projection which is based on the ellipsoidal version of the Albers Equal Area Conic (AEAC) projection. The projection has the following parameters: Datum: North American Datum 1983 (NAD83) Ellipsoid: GRS80 or WGS84 Origin: 111.000 degrees West Longitude 51.000 degrees North Latitude Standard Parallels: N 52° 30' 00" N 58° 30' 00" 7.1.5 Grid Description The data are gridded in 5 km intervals based on the projection given in section 7.1.4. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage This data set contained continuous data from 16-May-1994 to 20-September-1994; it includes the three summer IFC's: IFC-1 24-May -> 16-June IFC-2 19-July -> 10-August IFC-3 30-August -> 19-September 7.2.2 Temporal Coverage Map RSS-14 personnel were at each AMS site during 1994 IFC-2 collecting calibration data for the following days: AMS SITE SITE ARRIVE DATE DEPARTING DATE Designation -------------------------------------------------------------------------- Saskatoon SK 19 July 22 July Meadow Lake MD 19 July 21 July Nipawin NP 23 July 24 July Prince Albert National Park PA 24 July 26 July La Ronge LR 27 July 30 July Flin Flon FF 30 July 01 August The Pas TP 30 July 01 August Thompson Airport TH 01 August 04 August Nelson House NL 04 August 08 August Lynn Lake LL 06 August 07 August 7.2.3 Temporal Resolution The data are 30 minute averages. The AMS data were originally reported as 15- minute averages, but because the satellite data is collected every 30 minutes (on the hour and half-hour), this data set is comprises 30-minute averages. 7.3 Data Characteristics 7.3.1 Parameter/Variable Variable Also referred to as ------------------------------------------------ ------------------------------ 1 - Scaled Uncorrected Net Surface Radiation Rn 2 - Scaled Corrected Net Surface Radiation Rn-COR 3 - Scaled Shortwave down at surface Kdn 4 - Scaled Shortwave up at surface Kup 5 - Scaled Net Shortwave at surface K* 6 - Scaled Uncorrected Longwave down at surface Ldn 7 - Scaled Corrected Longwave down at surface Ldn-COR 8 - Scaled Uncorrected Longwave up at surface Lup 9 - Scaled Uncorrected Net Longwave at surface L* 10 - Scaled Corrected Net Longwave at surface L*-COR 11 - Scaled Uncorrected Net Radiation at surface L*+ GOES-derived K* 12 - Scaled Corrected Net Radiation at surface L*-COR+GOES-derived K* 13 - Scaled Optimal Net Radiation Optimal Net Radiation (2 & 12) 7.3.2 Variable Description/Definition Variable Wavelength Region ------------------------------------------------ ----------------- 1 - Scaled Uncorrected Net Surface Radiation (0.3 to 100.0 µm) 2 - Scaled Corrected Net Surface Radiation (0.3 to 100.0 µm) 3 - Scaled Shortwave down at surface (0.3 to 3.5 µm) 4 - Scaled Shortwave up at surface (0.3 to 3.5 µm) 5 - Scaled Net Shortwave at surface (0.3 to 3.5 µm) 6 - Scaled Uncorrected Longwave down at surface (4.0 to 100.0 µm) 7 - Scaled Corrected Longwave down at surface (4.0 to 100.0 µm) 8 - Scaled Uncorrected Longwave up at surface (4.0 to 100.0 µm) 9 - Scaled Uncorrected Net Longwave at surface (4.0 to 100.0 µm) 10 - Scaled Corrected Net Longwave at surface (4.0 to 100.0 µm) 11 - Scaled Uncorrected Net Radiation at surface (0.3 to 100.0 µm) 12 - Scaled Corrected Net Radiation at surface (0.3 to 100.0 µm) 13 - Scaled Optimal Net Radiation (0.3 to 100.0 µm) 7.3.3 Unit of Measurement Variable Units ------------------------------------------------ ---------- 1 - Scaled Uncorrected Net Surface Radiation [0.1 W/m2] 2 - Scaled Corrected Net Surface Radiation [0.1 W/m2] 3 - Scaled Shortwave down at surface [0.1 W/m2] 4 - Scaled Shortwave up at surface [0.1 W/m2] 5 - Scaled Net Shortwave at surface [0.1 W/m2] 6 - Scaled Uncorrected Longwave down at surface [0.1 W/m2] 7 - Scaled Corrected Longwave down at surface [0.1 W/m2] 8 - Scaled Uncorrected Longwave up at surface [0.1 W/m2] 9 - Scaled Uncorrected Net Longwave at surface [0.1 W/m2] 10 - Scaled Corrected Net Longwave at surface [0.1 W/m2] 11 - Scaled Uncorrected Net Radiation at surface [0.1 W/m2] 12 - Scaled Corrected Net Radiation at surface [0.1 W/m2] 13 - Scaled Optimal Net Radiation [0.1 W/m2] 7.3.4 Data Source Variable Source ------------------------------------------------ ------ 1 - Scaled Uncorrected Net Surface Radiation AMS 2 - Scaled Corrected Net Surface Radiation AMS* 3 - Scaled Shortwave down at surface AMS 4 - Scaled Shortwave up at surface AMS 5 - Scaled Net Shortwave at surface AMS 6 - Scaled Uncorrected Longwave down at surface AMS 7 - Scaled Corrected Longwave down at surface AMS* 8 - Scaled Uncorrected Longwave up at surface AMS 9 - Scaled Uncorrected Net Longwave at surface AMS 10 - Scaled Corrected Net Longwave at surface AMS* 11 - Scaled Uncorrected Net Radiation at surface AMS@ 12 - Scaled Corrected Net Radiation at surface AMS& 13 - Scaled Optimal Net Radiation AMS*& * Indicates data were first adjusted according to the calibrations conducted. @ Source also includes net solar radiation derived from GOES imagery & Source also includes net solar radiation derived from GOES imagery, and L* was first adjusted according to the calibrations conducted (L*-COR) 7.3.5 Data Range Variable Range (Approx.) ----------------------------------------------- ----------------- 1 - Scaled Uncorrected Net Surface Radiation -200 to 700 W/m2 2 - Scaled Corrected Net Surface Radiation -200 to 700 W/m2 3 - Scaled Shortwave down at surface to 1100 W/m2 4 - Scaled Shortwave up at surface 0 to 250 W/m2 5 - Scaled Net Shortwave at surface 0 to 850 W/m2 6 - Scaled Uncorrected Longwave down at surface 200 to 500 W/m2 7 - Scaled Corrected Longwave down at surface 200 to 500 W/m2 8 - Scaled Uncorrected Longwave up at surface 300 to 600 W/m2 9 - Scaled Uncorrected Net Longwave at surface -200 to 0 W/m2 10 - Scaled Corrected Net Longwave at surface -200 to 0 W/m2 11 - Scaled Uncorrected Net Radiation at surface -200 to 700 W/m2 12 - Scaled Corrected Net Radiation at surface -200 to 700 W/m2 13 - Scaled Optimal Net Radiation -200 to 700 W/m2 7.4 Sample Data Record The following is a sample header from one of the image data files: -----------------------------Begin Sample Header------------------------------ ** BOREAS LEVEL-2 GROUND RADIOMETER-BASED & MERGED RADIATION BUDGET PRODUCTS ** ------------------------------------------------------------------------------- Parameter Tape Block Contents Number Number 1 Header Record (This record) (Ascii Characters 1 2 Uncorrected Total Net (Rn ) (units=0.1 w/m*m) 2 3 Corrected Total Net (Rn-COR ) (units=0.1 w/m*m) 3 4 Solar Down (Kdn ) (units=0.1 w/m*m) 4 5 Solar Up (Kup ) (units=0.1 w/m*m) 5 6 Solar Net (K* ) (units=0.1 w/m*m) 6 7 Uncorrected Infrared Down (Ldn ) (units=0.1 w/m*m) 7 8 Corrected Infrared Down (Ldn-COR) (units=0.1 w/m*m) 8 9 Infrared Up (Lup ) (units=0.1 w/m*m) 9 10 Uncorrected Infrared Net (L* ) (units=0.1 w/m*m) 10 11 Corrected Infrared Net (L*-COR ) (units=0.1 w/m*m) 11 12 Uncorrected Total Net from Merged Products (units=0.1 w/m*m) (L* + GOES-derived K*) 12 13 Corrected Total Net from Merged Products (units=0.1 w/m*m) (L*-COR + GOES-derived K*) 13 14 Optimal Total Net from Parameters 2 & 12 (units=0.1 w/m*m) Bytes / Grid Cell : 2 Grid Cells/ Line : 78 Lines / Image : 78 Image data record : 12168 bytes = 2 bytes/cell x78 cells/line x 78 lines Tape Block Size : 12168 bytes E-W Resolution : 5 km N-S Resolution : 5 km Date : 06/30/94 Time (UTC) : 1630 Julian Day : 181 Parameter Stations Used for Objective Analysis 1 ff ll lr md nl np sk th tp 2 ff ll lr md nl np sk th tp 3 ff ll lr md nl np sk th tp 4 ff ll lr md nl np sk th tp 5 ff ll lr md nl np sk th tp 6 ff ll lr nl np th tp 7 ff ll lr nl np th tp 8 ff ll lr nl np th tp 9 ff ll lr md nl np sk th tp 10 ff ll lr md nl np sk th tp 11 Merged Product 12 Merged Product 13 Merged Product Year.......... 94 Month......... 6 Day........... 30 Hour.......... 16 Minute........ 30 Julian Day.... 181 -------------------------------End Sample Header------------------------------ *****NOTE***** In the above header record under "Parameter Stations Used for Objective Analysis," the station "pa" is not reporting for any parameter at that time. The station abbreviations stand for: ff -> Flin Flon ll -> Lynn Lake lr -> La Ronge md -> Meadow Lake nl -> Nelson House np -> Nipawin pa -> Prince Albert National Park sk -> Saskatoon th -> Thompson Airport tp -> The Pas To clarify, if a station abbreviation is listed under "Parameter Stations Used for Objective Analysis," that particular station is reporting that value at that time step. There was no minimum number of reporting stations for the objective analysis to run, rather it is up to the end user of these data to determine whether there are enough stations present to produce a good analysis. 8. Data Organization 8.1 Data Granularity The smallest orderable unit of data is one days worth of data, which would consist of 48 data files, one for each 30-minute period. 8.2 Data Format 8.2.1 Uncompressed Format All the gridded radiation image data are stored in 6144 files (48 files/day * 128 days). Each file contains 14 records of 12,168 bytes. The first record is an ASCII header record. Records 2-14 are a series of 13 image parameters for a given 30-minute time period. The series of records in the file are: Record Description 1 ASCII header information 2 Binary Scaled Uncorrected Net Radiation 3 Binary Scaled Corrected Net Radiation 4 Binary Scaled Shortwave Down 5 Binary Scaled Shortwave Up 6 Binary Scaled Net Shortwave 7 Binary Scaled Uncorrected Longwave Down 8 Binary Scaled Corrected Longwave Down 9 Binary Scaled Uncorrected Longwave Up 10 Binary Scaled Uncorrected Net Longwave 11 Binary Scaled Corrected Net Longwave 12 Binary Scaled Uncorrected Combined Net Radiation 13 Binary Scaled Corrected Combined Net Radiation 14 Binary Scaled Optimal Net Radiation The ASCII header record contains 156 logical records of 78 bytes each. Records 2 to 13 each contain 78 logical records (image lines) of 156 bytes. Each image line contains 78 2-byte (16-bit) values that represent the 78 pixels across the line. The 2-byte values are stored as low-order byte first. Software to read the files can be obtained by anonymous ftp at: metsat.met.fsu.edu in boreas/Station_grid_products 8.2.2 Compressed Format The image files been compressed with the Gzip (GNU zip) compression program (file_name.gz). These data have been compressed using gzip version 1.2.4 and the high compression (-9) option (Copyright (C) 1992-1993 Jean-loup Gailly). Gzip uses the Lempel-Ziv algorithm (Welch, 1994) also used in the zip and PKZIP programs. The compressed files may be uncompressed using gzip (with the -d option) or gunzip. Gzip is available from many websites (for example, the ftp site prep.ai.mit.edu/pub/gnu/gzip-*.*) for a variety of operating systems in both executable and source code form. Versions of the decompression software for various systems are included on the CD-ROMs. 9. Data Manipulations Only AMS data were used. Those parameters that DO NOT include a "-COR" were taken directly from the AMS data base and were not altered in any way. For example, parameter Rn is the direct measurement of net radiation at all the sites, interpolated onto the standard BOREAS grid. Those parameters that DO contain the designation "-COR" have been altered before being interpolated onto the grid. For example, to get Rn-COR, the Rn data set at each site first had the calibrations applied and then were interpolated onto the grid. Similarly, L*- COR was extracted from Rn-COR by subtracting K*, i.e., L*-COR = Rn-COR - K*. Parameters 11 and 12 (Records 12 and 13) are GOES-based values of net radiation. That is, using L* extracted from the net radiation measurements and adding this to K* derived from GOES satellite imagery results in a GOES-based field of net radiation. Direct measurements of L* were not used because too few of the sites were measuring downwelling or emitted longwave radiation to produce good results during the objective analysis. Parameter 13 (Record 14) is what is known as "Optimal Net Radiation." This parameter was arrived at by fusing parameters 2 and 12 (Records 3 and 13). The idea behind this parameter is that it will combine the optimal properties of the two parameters, thereby producing an optimal field. The fusing process provides more weight to parameter 2 (Record 3) at grid points close to a measurement site. The weighting scheme gives progressively larger weights to parameter 12 (Record 13) as the distance from a measurement site increases, and vice versa for parameter 2 (Record 3). The corrected measurements of Rn in the direct vicinity of each AMS site are more accurate than the GOES-based estimates of Rn at the same location. However, the GOES-based measurements better represent the between-site gradients of the net radiation field. By combining the two parameters with a distance-based weighting function, it is hoped that an optimal field (in both gradient and measurement accuracy) is produced. 9.1 Formulae Rn = K* + L* net_radiation = net_shortwave_radiation + net_longwave_radiation K* = K_down - K_up L* = L_down - L_up Upwelling longwave radiation was calculated from the surface temperature retrieved from the Everest/4000 IRT using the following equation: I = e * s * T4 (Stefan-Boltzmann Law) e emissivity s Stefan-Boltzmann constant T temperature K_down incoming solar radiation K_up reflected solar radiation L_down downwelling longwave radiation (emitted by atmosphere) L_up upwelling longwave radiation (emitted by Earth) 9.1.1 Derivation Techniques and Algorithms No special derivation techniques or algorithms were used. 9.2 Data Processing Sequence 9.2.1 Processing Steps 1. All the AMS net radiometers were calibrated. 2. The new calibrations were applied to the AMS Rn data set for IFC-1, 2, and 3. 3. L* was extracted from the Rn values (and corrected Rn values). 4. Other AMS radiation parameters, such as K_down and K_up, were retrieved. 5. GOES-retrieved values of K* were combined with L* to produce a new Rn. 6. An objective analysis procedure was applied to the data. 7. The gridded data sets were then converted to binary format. NOTE: Objective Analysis Procedure The objective analysis scheme incorporates a weighting function based on the distance d(i) of any given measuring site i to any grid point. The weights assigned to the individual net pyrradiometer measurements are based on the inverse squares of the d(i)'s, i.e., the set of weights are given by the set of all d(i)-2. Thus, at each grid point, the objective analysis scheme calculates a weighted average value for that point based on all surrounding net radiation measurements within a cutoff distance d(max), using the inverse distance-square station weights. Closer stations thus get the largest weights. A grid mesh of 5 km was selected and the d(max) parameter assigned to 100 km. Sensitivity tests were performed by removing various stations and reanalyzing and by doing so with different sizes for d(max). These tests demonstrate that the resultant objectively analyzed fields are not particularly sensitive to changes in the analysis design. Subjective (hand) analyses of the net radiation field were also compared with results from the computer analysis. Both sets of analyses were in close agreement. These tests indicate that the interpretation of the intercomparison results should not be meaningfully affected by the objective analysis design. BORIS personnel processed the data by: 1) Extracting and verifying header information from each file to inventory the data in the on-line data base 2) Compressing the files for distribution on CD-ROM. 9.2.2 Processing Changes No noteworthy processing changes were made. 9.3 Calculations 9.3.1 Special Corrections/Adjustments The 15-minute average AMS data had to be averaged to 30 minutes to be compatible with the satellite images, which are available only on the hour and half hour. 9.3.2 Calculated Variables Parameters 12 and 13 (the merged, or optimal, products) were the only calculated variables. A weighting function, based strictly on distance from the nearest AMS station, was used for the calculation(s). For a grid point at or very near an AMS station, the value is essentially the value measured at the station. As the distance from the station increases, the weighting of the satellite-based value of net radiation increases and the weighting of the point measurement, or value measured at the nearest AMS site, decreases. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error There are a few things users should be cognizant of before using these data. •The pre- and post-field calibrations of the transfer instruments varied on the order of 5%. It is not known if this change is the result of an actual calibration drift or the result of differing atmospheric conditions during the pre- and post-field calibrations. Even with these changes, these calibrations are still believed to be an improvement. •The satellite-based values of net radiation are a combination of L* extracted from net pyrradiometer measurements of net radiation and satellite-retrieved values of net solar radiation. Hodges and Smith (1997) examined only the hours around solar noon (+/- 3 hours around solar noon). This reduced errors from the combination of the two data sets since L* is typically 10% of K* at these times. However, for this data set, the satellite-based values are available from sunrise to sunset (nighttime values of the satellite-based measurements are only net pyrradiometer measurements of net radiation). •One must also realize that the satellite-based values of net radiation are a combination of 30-,minute averaged data (L*) and instantaneous snapshots of the conditions on the hour and half-hour. On a clear day errors resulting from this combination will be small; however, under cloudy or convective conditions, errors could be significant. •While at the Lynn Lake AMS site, the AMS datalogger was not operating as a result of lightning prior to the team’s arrival. As a result, a calibration factor was not found for this site's instrument. For the corrected parameters in this data set (such as Rn-COR), an average correction was used for the Lynn Lake data. That is, the correction factors at the nine other AMS sites were averaged to produce a correction factor for Lynn Lake. •Users of this data set should be cognizant of the "Parameter Stations Used for Objective Analysis" section in each file header. In the end, it was decided in the creation of this data set NOT to include a minimum number of stations required for the objective analysis to run, but instead, to have it run no matter how many stations were reporting and to provide a list of the reporting stations. This way the user can decide for him or herself whether a missing station(s) will affect the analysis. 10.2 Quality Assessment 10.2.1 Data Validation by Source Because no other gridded data sets of these fields were available at the time of their creation, no comparisons of the gridded fields were done. Extensive validation has been done with the surface net solar algorithm used to retrieve surface fluxes from GOES data with ground measurements. The interested reader should consult Gu and Smith (1997) for these details. Subjective (hand) analyses at several time steps were compared with the results of the objective analysis, with very good agreement. 10.2.2 Confidence Level/Accuracy Judgment Overall, satisfaction with this data set is pretty good. What a person should keep in mind, however, is the inaccuracy of the net pyrradiometers themselves. RSS-14 is confident that the calibrations performed improved the accuracy of the measurements, but how close they are to being "correct" is unknown. At the very least, they all were calibrated to a single source instead of all having independent calibrations. (Smith, et. al., 1997, have shown that the percentage spread in measured values can vary substantially when the original factor calibrations are used.) 10.2.3 Measurement Error for Parameters At this time, quantitative errors cannot be placed on the data set. Because the "real" values of net radiation are just not known, it is necessary to wait for the reaction of modelers to the data set to see if in fact these data are an improvement. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center Not applicable. 11. Notes 11.1 Limitations of the Data Users should be careful about using data near the boundaries, especially in the NE portion (which includes some of the NSA), since portions are outside of the domain of the AMS network and extrapolation errors are likely greater in this region. 11.2 Known Problems with the Data There are no known problems per se; however, one should be cognizant of the issues discussed in Section 10. 11.3 Usage Guidance Users should proceed with caution, and understand the discussion in Section 10.1. Before uncompressing the Gzip files on CD-ROM, be sure that you have enough disk space to hold the uncompressed data files. Then use the appropriate decompression program provided on the CD-ROM for your specific system. 11.4 Other Relevant Information None given. 12. Application of the Data Set Energy budget modelers should find this data set useful, especially if they are interested in between-site values. 13. Future Modifications and Plans No future updates or modifications are planned for these data. 14. Software 14.1 Software Description Software is available to assist in reading the files. Gzip (GNU zip) uses the Lempel-Ziv algorithm (Welch, 1994) used in the zip and PKZIP commands. 14.2 Software Access Software for reading the data are available by anonymous ftp at metsat.met.fsu.edu in boreas/Station_grid_products. Gzip is available from many websites across the net (for example) ftp site prep.ai.mit.edu/pub/gnu/gzip-*.*) for a variety of operating systems in both executable and source code form. Versions of the decompression software for various systems are included on the CD-ROMs. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or FAX. 15.4 Data Center Status/Plans The BOREAS RSS-14 gridded radiometer and surface radiation images are processed and sufficiently quality checked, they will be available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory Oak Ridge, TN (423) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products This data set is available on 8 mm tape. 16.2 Film Products None. 16.3 Other Products None. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Radiation and Energy Balance Systems, Inc. Q*6 Instruction Manual. The Eppley Laboratory, Inc. Instruction Manuals for the PSP, PIR, and Everest IRT. Welch, T.A. 1984, A Technique for High Performance Data Compression, IEEE Computer, Vol. 17, No. 6, pp. 8 - 19. 17.2 Journal Articles and Study Reports Gu, J. and E.A. Smith. 1997: High resolution estimates of total solar and PAR surface fluxes over large scale BOREAS study area from GOES measurements. J. Geophys. Res., BOREAS Special Issue. v. 102(D24):29,685-29,705. Hodges, G.B. and E.A. Smith. 1997. Intercalibration, objective analysis, intercomparison and synthesis of BOREAS surface net radiation measurements. J. Geophys. Res., BOREAS Special Issue, v. 102(D24):28,885-28,900. Hodges, G.B. 1997. Synthesis of BOREAS surface net radiation measurements. M.S. Thesis, Dept. of Meteorology, Florida State University, 68 pp. Hodges, G.B. and E.A. Smith. 1996. Optimal estimates of surface net radiation field over BOREAS study-area from combination of net radiometer point measurements and GOES satellite retrievals. Eighth Conf. on Sat. Met. & Ocean. Amer. Met. Soc., Boston, MA. pp. 464-465. Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P. and F. Hall, K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P.and F. Hall, K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P.J., F.G. Hall, R.D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan, K.J. Ranson, P.M. Crill, D.P. Lettenmaier, H. Margolis, J. Cihlar, J. Newcomer, D. Fitzjarrald, P.G. Jarvis, S.T. Gower, D. Halliwell, D. Williams, B. Goodison, D.E. Wickland, and F.E. Guertin. (1997). "BOREAS in 1997: Experiment Overview, Scientific Results and Future Directions", Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28731-28770. Smith, E.A., G.B. Hodges, M. Bacrania, H.J. Cooper, M.A. Owens, R. Chappell, and W. Kincannon. 1997: BOREAS net radiometer engineering study. NASA Report under Grant NAG5-2447. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms net pyrradiometer - Instrument that measures net radiation pyrradiometer - Instrument that measures shortwave radiation pyrgeometer - Instrument that measures longwave radiation Rn - Net radiation. Defined as (Rn = K_down - Kup + L_down - L_up) K_down - Incoming solar radiation, downwelling solar radiation, etc K_up - Reflected solar radiation. The K_down that has been reflected. K* - Net solar radiation. K* = K_down - K_up L_down - Longwave (IR) radiation emitted by the atmosphere. Downwelling IR. L_up - Longwave (IR) radiation emitted by the earth. Upwelling IR. L* - Net longwave radiation. L* = L_down - L_up 19. List of Acronyms AEAC - Alber Equal Area Conic AFM - Airborn Fluxes and Meteorology AMS - Automatic Meteorological Station ASCII - American Standard Code for Information Exchange BOREAS- BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center DAT - Digital Archive Tape EOS - Earth Observing System EOSDIS- EOS Data and Information System GOES - Geosynchronous Operational Environmental Satellite GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign IR - Infrared Radiation (longwave radiation) IRT - Infrared Thermometer NAD83 - North American Datum 1983 NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park PIR - Precision Infrared Radiometer PSP - Precision Spectral Pyranometer REBS - Radiation and Energy Balance Systems RSS - Remote Sensing Science SSA - Southern Study Area TF - Tower Flux URL - Uniform Resource Locator VIS - Visible WRR - World Radiometric Reference 20. Document Information 20.1 Document Revision Date(s) Written: 22-Dec-1997 Last Updated: 14-Sep-1998 20.2 Document Review Date(s) BORIS Review: 16-Jan-1998 Science Review: 20.3 Document 20.4 Citation Dr. Eric A. Smith, Dept. of Meteorology, Florida State University should be acknowledged when this data set is referenced or used by another investigator. Additionally, the following papers should be cited: Hodges, G.B. and E.A. Smith. 1997. Intercalibration, objective analysis, intercomparison and synthesis of BOREAS surface net radiation measurements. J. Geophys. Res., BOREAS Special Issue, v. 102(D24):28,885-28,900. Gu, J. and E.A. Smith. 1997. High resolution estimates of total solar and PAR surface fluxes over large scale BOREAS study area from GOES measurements. J. Geophys. Res., BOREAS Special Issue, v. 102(D24):29,685-29,705. 20.5 Document Curator 20.6 Document URL Keywords: net radiation solar radiation longwave radiation terrestrial radiation energy balance net radiometer net pyrradiometer pyranometer pyrgeometer gridded data set calibration GOES Eppley REBS RSS14_L3_Gridded_SRB.doc 09/14/98