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 networks domain).

The spatial coverage of this data set is a parallelogram with the corners:

          Latitude     Longitude    BOREAS X   BOREAS Y
-> NW    56.57772N   101.60420W     575        660
-> NE    55.96247N    95.47948W     960        660
-> SW    53.43708N   108.13830W     190        275
-> SE    53.15204N   102.37890W     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 m)
2  - Scaled Corrected Net Surface Radiation  	(0.3 to 100.0 m)
3  - Scaled Shortwave down at surface 	(0.3 to 3.5 m)
4  - Scaled Shortwave up at surface  	(0.3 to 3.5 m)
5  - Scaled Net Shortwave at surface  	(0.3 to 3.5 m)
6  - Scaled Uncorrected Longwave down at surface  	(4.0 to 100.0 m)
7  - Scaled Corrected Longwave down at surface  	(4.0 to 100.0 m)
8  - Scaled Uncorrected Longwave up at surface  	(4.0 to 100.0 m)
9  - Scaled Uncorrected Net Longwave at surface  	(4.0 to 100.0 m)
10 - Scaled Corrected Net Longwave at surface  	(4.0 to 100.0 m)
11 - Scaled Uncorrected Net Radiation at surface  	(0.3 to 100.0 m)
12 - Scaled Corrected Net Radiation at surface  	(0.3 to 100.0 m)
13 - Scaled Optimal Net Radiation  	(0.3 to 100.0 m)

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 teams 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