DQRID : D981109.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
08/16/1998165008/16/19981730Suspect
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Subject:
SGP/GRAMS - Non-standard data
DataStreams:sgpgramsftsbbrC1.00, sgpgramsftsbbrC1.a0
Description:
Experiment with GRAMS at ARM Southern Great Plains  Central Facility between 1650 UTC 
(1150 L) and 1730 UTC (1230 L) on August 16, 1998

Users of the GRAMS instrument deployed in the field at the CF should be informed that a 
shading experiment was conducted with the instrument by Thomas P. Charlock and Seiji Kato 
1650-1730 UTC on August 16, 1998.

Some of the GRAMS data in the interval 1659-1721 UTC should be affected substantially; 
they should NOT be used as typical GRAMS observations.  This note explains the experiment 
and indicates how they can be used.  The experiment provides brief periods during which the 
white portion of the instrument (the part under the dome that feeds the detector) is
	a) shaded from the direct solar beam but
	b) still bathed in diffuse solar radiation.
During part of the experminent a small hand held shade was used to cast a shadow on the 
dome of each of the two GRAMS instruments.  GE (GW) denotes the GRAMS instrument on the 
east (west) of the hardened cooling case.  I assume that GE (GW) is the broadband 
(narrowband) instrument. The GRAMS TDDR, which has its own shadowband, was not present; this 
experiment did not call for the removal of the TDDR.  When a shadow was cast on GE, the other 
instrument (GW) was not in the shadow; and vice versa.

The shade (diameter 10 cm) was blackened and cylindrical. The shade was held approximately 
1 m from the respective dome that was shaded.  The shade was attached to a blackened 
plastic pole (diameter 2 cm; length 2.5 m).  Shading was done by hand from a step ladder; 
the pole was not supported by the ground; a 10-15 pmh wind caused some vibration of the 
shade. GE was shaded for 5 minutes; then the shade was moved to GW for 5 minutes;a second 
5-minute shading for GE followed; and finally a second 5-minute shading for GW.

Q.: What data is provided by this experiment?
A.:  For nearly clear conditions, there are two intervals of three minutes each during 
which GE is shaded from the direct beam of the sun (but still illuminated by most of the 
diffuse solar flux); GE is shaded without interuption during 17:01:00-17:04:00 and 
17:11:00-17:14:00 UTC on 16 August 1998.  For the same conditions, there are two OTHER intervals 
of three minutes each during which GW is shaded from the direct beam of the sun (but still 
illuminated by most of the diffuse solar flux); GW is shaded without interuption during 
17:06-17:09:00 and 17:16:00-17:19:00 UTC on 16 August 1998.
     
Q.:  What is the scientlific utility of the data from this experiment?
The experiment provides of a near-clear sky record of the broadband shortwave (SW) 
measured by GRAMS under the special condition of shading; the direct component of the beam has 
been removed, providing an ad hoc observation of the diffuse solar irradiance at the 
surface.  Several theoreticians have maintained that they cannot adequately simulate the 
measurements of  diffuse solar irradiance under clear skies at ARM CART SGP made with Eppley 
radiometers.  This experiment provides another target for theoreticians: a provisional 
estimate from GRAMS, a later generation technology developed by Dr. Franciso Valero and his 
colleagues at Scripps and NASA Ames.  The specific ad hoc shading procedure used in this 
experiment has not been reviewed.

Log of GRAMS experiment on August 16, 1998

This experiment was done with sky coverage of 1-5 0.000000or very thin cumulus. The 
cumulus did not obscure the sun.  A thin cirrus or haze was barely visible, below and to the 
right of the sun; it could be seen over less than 50f the sky.

1650-1659 UTC  general set up aeround GRAMS, which is about 2 m above he surface.  Minimal 
effect on GRAMS is anticipated.  A step ladder (~1.9m) is placed ~1.5m to the east of 
GRAMS.
     
1659-1700 UTC  both GE and GW unshaded.  Because the hand-held shade may have been placed 
on GE one or two seconds early (i.e., 16:59:59 UTC), the data for the one minute interval 
1659-1700 (16:59:00-17:00:00) can be regarded as suspect.
     
1700-1701 UTC a shadow is cast on GE at the start of this interval. Because the hand-held 
shade may have been placed on GE one or two seconds late (i.e., 17:00:01 UTC), the data 
for the one minute interval 1700-1701 (17:00:00-17:01:00) can be regarded as suspect.  
There is no shadow on GW.
     
1701-1704 UTC a shadow is cast on GE continuously.  The entire dome of GE is shaded for 
all but possibly few brief seconds for the three-minute interval (17:01:00-17:04:00).  The 
white section in the center of the dome is shaded without interruption.  No shadow falls 
on GW.
     
1704-1705 UTC a shadow is cast on GE, but the shade moves to GW at the very end of this 
interval.   Because the hand-held shade may have been moved one or two seconds early or 
late (i.e., 17:04:59 UTC), the data for the one minute interval 1704-1705 
(17:04:00-17:05:00) can be regarded as suspect for both GE and GW.
     
1705-1706 UTC a shadow is cast on GW at the start of this interval. Because the hand-held 
shade may have been placed on GW one or two seconds late (i.e., 17:05:01 UTC), the data 
for the one minute interval 1705-1710 (17:05:00-17:10:00) can be regarded as suspect for 
both GE and GW. When the shadow is cast on GW with the 10 cm shade, the pole (diameter 2 
cm) sometimes casts a shadow on the dome of GE, but then no shadow is cast on the white 
center of GE.
     
1706-1709 UTC a shadow is cast on GW continuously.  The entire dome of GW is shaded for 
all but possibly few brief seconds for the three-minute interval (17:06:00-17:09:00).  The 
white section in the center of the dome of GW is shaded without interruption.  As the 
shadow is cast on GW with the 10 cm shade, the pole (diameter 2 cm) sometimes casts a shadow 
on the dome of GE, but then no shadow is cast on the white center of GE.
     
1709-1710 UTC a shadow is cast on GW, but the shade moves to GE at the very end of this 
interval.   Because the hand-held shade may have been moved one or two seconds early or 
late (i.e., 17:09:59 UTC), the data for the one minute interval 1709-1710 
(17:09:00-17:10:00) can be regarded as suspect for both GE and GW. As the shadow is cast on GW with the 10 
cm shade, the pole (diameter 2 cm) sometimes casts a shadow on the dome of GE, but then 
no shadow is cast on the white center of GE.
     
1710-1711 UTC a shadow is cast on GE at the start of this interval.  During this interval, 
the second operator begins to tend the shade.  Because the hand-held shade may have been 
placed on GE/removed from GW several seconds late (i.e., 17:10:05 UTC), the data for the 
one minute interval 1710-1711 can be regarded as suspect for both GE and GW.  When GE is 
shaded, there is no shadow on GW.
     
1711-14 UTC a shadow is cast on GE continuously.  The entire dome of GE is shaded for all 
but possibly few brief seconds for the three-minute interval.  The white section in the 
center of the dome is shaded without interruption.  No shadow falls on GW.
     
1714-1715 UTC a shadow is cast on GE, but the shade moves to GW at the very end of this 
interval.   Because the hand-held shade may have been moved one or two seconds early or 
late, the data for the one minute interval 1714-1715 can be regarded as suspect for both GE 
and GW.
     
1715-1716 UTC a shadow is cast on GW at the start of this interval. Because the hand-held 
shade may have been placed on GW one or two seconds late, the data for the one minute 
interval 1705-1710 can be regarded as suspect for both GE and GW.  When the shadow is cast 
on GW with the 10 cm shade, the pole (diameter 2 cm) sometimes casts a shadow on the dome 
of GE, but then no shadow is cast on the white center of GE.
     
1716-1719 UTC a shadow is cast on GW continuously.  The entire dome of GW is shaded for 
all but possibly few brief seconds for the three-minute interval.  The white section in the 
center of the dome of GW is shaded without interruption.  As the shadow is cast on GW 
with the 10 cm shade, the pole (diameter 2 cm) sometimes casts a shadow on the dome of GE, 
but then no shadow is cast on the white center of GE.
     
1719-1720 UTC a shadow is cast on GW, but the shade is completely removed from both GW and 
GE at the very end of this interval.   Because the hand-held shade may have been moved 
one or two seconds early or late, the data for the one minute interval 1719-1720 can be 
regarded as suspect for both GE and GW. As the shadow is cast on GW with the 10 cm shade, 
the pole (diameter 2 cm) sometimes casts a shadow on the dome of GE, but then no shadow is 
cast on the white center of GE.
     
1720-1730 UTC all equipment for this experiment is removed from the vicinitiy of GRAMS.
Suggestions: 
Measurements:sgpgramsftsbbrC1.a0:
  • motor
  • base_time
  • alt
  • fsbr_signal
  • fsbr_temp_count
  • tsbr_signal
  • lat
  • time_offset
  • tsbr_temp_count
  • cover
  • blower
  • system_temp
  • lon
more
sgpgramsftsbbrC1.00:
  • Raw data stream - documentation not supported
more

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