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Known Data Irregularities

Indian Ocean Gap Artifact

There is a visible and common artifact in much of the data set period, due to a lack of coverage from geostationary satellites over an area centered on 70 degrees east longitude. This situation, commonly called the Indian Ocean gap, occurs for all of the July 1983 – June 1998 time period, except for April 1988 – March 1989, when data from the INSAT satellite is available to cover the gap. In July of 1998, Meteosat-5 was moved over the gap area, eliminating the gap.

When the Indian Ocean gap occurs, the gap area is covered by polar orbiting satellites, which can result in only one or two daytime overpasses per day. Geosynchronous temporal sampling during the daytime is 3-5 times per daytime depending upon the latitude (between 55 degrees North and South) and the time of year.

In addition to the gap itself, the areas on the edges of the Meteosat and GMS satellite coverage areas rely on low satellite view angles and therefore generally show a bias towards higher cloud amounts. This is further manifested in SRB flux fields, as areas in the gap show higher shortwave fluxes at the surface than the nearby areas on the Meteosat and GMS edges.

Image of shortwave down at the surface for June 1998

Image of shortwave down at the surface for July 1998

Once the gap was covered by geostationary satellites, the affect on the amount of filling in cloud properties and fluxes is noticeable. While the India gap isn’t the only contributing factor, it is obvious in the following picture that it is a major factor in the filling. Temporal variability of the SRB fluxes is expected to be higher prior to July 1998.

Image of filled properties

Satellite Calibration Shifts

The SRB algorithms rely heavily on radiances and cloud properties from ISCCP. Great care is taken by the ISCCP team to produce a well-calibrated, homogeneous dataset from dozens of satellites over the course of several decades. However, there are a few known issues and discontinuities in the ISCCP products which are likely to be reflected in SRB products.

ISCCP uses a reference afternoon polar orbiter as a calibration standard for the other satellites (geostationary and polar orbiting) in the constellation. The afternoon orbiters are subject to orbital drift and are replaced every few years. The dates of transition from one reference satellite to the next are particular dates where small discontinuities in the SRB products are possible. The transition dates are as follows:

  • February 1, 1985: NOAA-7 replaced by NOAA-9
  • November 1, 1988: NOAA-9 replaced by NOAA-11
  • September 30, 1994: NOAA-11 goes out of service
  • February 1, 1995: NOAA-14 goes into service

For the October 1994-January 1995 timeframe there was no reference orbiter available, so an interpolation between NOAA-11 and NOAA-14 is used. SRB results show noticeable anomalies in this period, some of which are likely artifacts of the calibration situation.

  • October 1, 2001: NOAA-14 replaced by NOAA-16
  • January 1, 2006: NOAA-16 replaced by NOAA-18

From NOAA-16 onward, the visible calibration is bi-linear, which has led to some changes from the previous linear calibrations. The 2001 transition to NOAA-16 is accompanied by fairly strong radiance increases over ice, which has led to polar values of SRB surface albedo and cloud optical thickness which are probably anomalously high, and surface downward fluxes which may be too low. The NOAA-18 calibration appears to be raising overall reported visible radiances, especially reducing the frequency of very low radiance scenes, such as clear skies over ocean near the day-night terminator. The effect on SRB products from 2006 onward has been mainly to cause a jump in surface albedo over much of the planet. Surface downward fluxes are less affected.

Care should be taken when computing long term time series from SRB data, with special notice taken of known transition dates, including those noted.

TOVS Algorithm Change

The operational TOVS algorithm changed on October 1, 2001. This affects the surface skin temperature from the ISCCP project used in the primary longwave algorithm. While the algorithm normally uses the GEOS-4 surface skin temperature, the ISCCP surface skin temperature is used in place of the GEOS-4 temperature over land with total cloud amounts less than 50% and also under the condition of ice or snow coverage greater than 80%. Long-term deseasonalized trends of clear-sky and all-sky upward surface fluxes show an abrupt increase in the fluxes at the time of the change that continues to the end of the data record.

  • CAPABLE/CRAVE Full Site Photo from left to right site enclosures: 1196A NASA LaRC, MPLnet, Virginia DEQ
    CAPABLE/CRAVE Full Site Photo from left to right site enclosures: 1196A NASA LaRC, MPLnet, Virginia DEQ

  • NASA LaRC NAST-I and HU ASSIST side-by-side for intercomparison
    NASA LaRC NAST-I and HU ASSIST side-by-side for intercomparison

  • Virginia DEQ, NASA and Penn State-NATIVE Enclosures (from right to left)
    Virginia DEQ, NASA and Penn State-NATIVE Enclosures (from right to left)

  • Ozone-sonde away.
    Ozone-sonde away.
  • About to lift.
    About to lift.
PurpleAir PA-II-SD Air Quality Sensor
Laser Particle Counters
Type (2) PMS5003
Range of measurement 0.3, 0.5, 1.0, 2.5, 5.0, & 10 μm
Counting efficiency 50% at 0.3μm & 98% at ≥0.5μm
Effective range
(PM2.5 standard)*
0 to 500 μg/m³
Maximum range (PM2.5 standard)* ≥1000 μg/m³
Maximum consistency error (PM2.5 standard) ±10% at 100 to 500μg/m³ & ±10μg/m³ at 0 to 100μg/m³
Standard Volume 0.1 Litre
Single response time ≤1 second
Total response time ≤10 seconds
Pressure, Temperature, & Humidity Sensor
Type BME280
Temperature range -40°F to 185°F (-40°C to 85°C)
Pressure range 300 to 1100 hPa
Humidity Response time (τ63%): 1 s
Accuracy tolerance: ±3% RH
Hysteresis: ≤2% RH

Pandora capabilities










Total Column O3, NO2, HCHO, SO2, H2O, BrO

0.01 DU

0.1 DU



Virginia Department of Environment Quality in-situ instrumentation






Thermo Scientific 42C (Molybdenum converter)

60 s

NO and NOx

50 pptv


Teledyne API 200EU w/ photolytic converter
(EPA) PI-Szykman

20 s


50 pptv


Thermo Scientific 49C (VADEQ)

20 s


1 ppbv


Thermo Scientific 48i (VADEQ)

60 s


40 ppbv


Thermo Scientific 43i (VADEQ)

80 s


0.2 ppbv


Thermo Scientific 1400AB TEOM (VADEQ)

600 s

PM2.5 (continuous)


1 3%

Thermo Scientific Partisol Plus 2025 (VADEQ)

24 hr

PM2.5 (filter-based FRM)- 1/3 days



Large area view.
Latitude: 37.1038
Longitude: -76.3872
Elevation: 3 m Above sea level
Scenes: urban, marsh, bay, river and farm.


  • The inner red circle is a 20km CERES foot print centered on the BSRN-LRC site.
  • The pink circle represents a possible tangential 20km foot print.
  • The middle red circle represents the area in which a 20km foot print could fall and still see the site.
  • Yellow is a sample 40 deg off nadir foot print.
  • The outer red circle is the region which would be seen by a possible 40 deg off nadir foot print.
The BSRN-LRC sun tracker at the NASA Langley Research Center on a snowy day (02/20/2015) The BSRN-LRC sun tracker at the NASA Langley Research Center on a snowy day (02/20/2015)
CAPABLE-BSRN Google Site Location Image

Team Satellite Sensor G/L Dates Number of obs Phase angle range (°)
CMA FY-3C MERSI LEO 2013-2014 9 [43 57]
CMA FY-2D VISSR GEO 2007-2014
CMA FY-2E VISSR GEO 2010-2014
CMA FY-2F VISSR GEO 2012-2014
JMA MTSAT-2 IMAGER GEO 2010-2013 62 [-138,147]
JMA GMS5 VISSR GEO 1995-2003 50 [-94,96]
JMA Himawari-8 AHI GEO 2014- -
EUMETSAT MSG1 SEVIRI GEO 2003-2014 380/43 [-150,152]
EUMETSAT MSG2 SEVIRI GEO 2006-2014 312/54 [-147,150]
EUMETSAT MSG3 SEVIRI GEO 2013-2014 45/7 [-144,143]
EUMETSAT MET7 MVIRI GEO 1998-2014 128 [-147,144]
CNES Pleiades-1A PHR LEO 2012 10 [+/-40]
CNES Pleiades-1B PHR LEO 2013-2014 10 [+/-40]
NASA-MODIS Terra MODIS LEO 2000-2014 136 [54,56]
NASA-MODIS Aqua MODIS LEO 2002-2014 117 [-54,-56]
NASA-VIIRS NPP VIIRS LEO 2012-2014 20 [50,52]
NASA-OBPG SeaStar SeaWiFS LEO 1997-2010 204 (<10, [27-66])
NASA/USGS Landsat-8 OLI LEO 2013-2014 3 [-7]
NOAA-STAR NPP VIIRS LEO 2011-2014 19 [-52,-50]
NOAA GOES-10 IMAGER GEO 1998-2006 33 [-66, 81]
NOAA GOES-11 IMAGER GEO 2006-2007 10 [-62, 57]
NOAA GOES-12 IMAGER GEO 2003-2010 49 [-83, 66]
NOAA GOES-15 IMAGER GEO 2012-2013 28 [-52, 69]
VITO Proba-V VGT-P LEO 2013-2014 25 [-7]
KMA COMS MI GEO 2010-2014 60
AIST Terra ASTER LEO 1999-2014 1 -27.7
ISRO OceanSat2 OCM-2 LEO 2009-2014 2

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