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INSTRUMENT

Global Survey

TES has two basic science operating modes: Global Surveys and Special Observations. Global surveys are the routine observations that TES conducts approximately every two days, which produce "standard products." Special (Research) Observations include all other measurements, including those of validation and such events as volcano eruptions and biomass burning.

The at-launch version of the global survey consisted of a space view and a blackbody view calibration pair, two nadir views, and three limb tangents projected to the ground. On May 25, 2005, the global survey was modified to conserve instrument life. The three limb scans were eliminated from the sequences and replaced by an additional nadir scan.

Characteristics of Global Survey

  • An entire survey requires 16 orbits (about 26 hours).
  • 72 sequences are acquired on each orbit, triggered by passage of the orbital southern apex, which ensures that the same locations are observed repeatedly for the lifetime of the mission.
  • Each sequence requires 81.9 seconds to accomplish.
  • Each survey is preceded and followed by 2 orbits of pure space and blackbody views for calibration purposes.
  • Until June of 2008, Global Survey measurements cover 82(deg) S to 82(deg) N latitude. After this time, the latitudinal range of observations is revised in order to conserve instrument lifetime.

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Global Surveys are made on roughly a "one day on, one day off" cycle. The "off" periods are available for Special Observations. If no Special Observations are needed, TES rests to avoid wear and tear on the mechanical components and extend the life of the instrument. The Aura orbit repeats every 16 days (every 233 orbits), which can be divided into eight TES cycles, each of which takes about 2 days. Each cycle consists of the following measurements:

  • 2 orbits of global survey pre-calibration
  • 16 orbits of global survey
  • 2 orbits of global survey post-calibration
  • 9 orbits of special observation opportunities (except the 8th cycle, which has 10 orbits of special observations)

Except for emergencies, Global Surveys are never interrupted (e.g., by Special Operations). If a pre-planned event (e.g., a spacecraft maneuver or orbit adjustment) would interrupt a Global Survey, the survey is skipped in its entirety.

The following tables describe the spectral ranges of the filters used for Global Survey measurements.

Range of Optical Filters used for Nadir Global Survey Observations
  Focal Plane 2B Focal Plane 1B Focal Plane 2A Focal Plane 1A
Nadir-1 and Nadir-2 650-900 cm-1 950-1150 cm-1 1100-1325 cm-1 1900-2250 cm-1

Range of Optical Filters used for Limb Global Survey Observations
  Focal Plane 2B Focal Plane 1B Focal Plane 2A Focal Plane 1A
Filters Used
Limb-1 2B1 1B1 2A1 1A1
  650-900 cm-1 820-1050 cm-1 1100-1325 cm-1 1900-2250 cm-1
Limb-2 2B1 1B2 2A4 1A1
  650-900 cm-1 950-1150 cm-1 1700-1950 cm-1 1900-2250 cm-1
Limb-3 2B1 1B2 2A4 1A1
  650-900 cm-1 950-1150 cm-1 1700-1950 cm-1 1900-2250 cm-1

The tables below list the retrieved species (TES L2 standard products) from Global Survey Observations.

Species Retrieved from Nadir Global Survey Observations
Swath Objects H2O O3 CH4 CO NO2 HNO3 AtmT
Nadir 1 and 2 X X X X     X

Species Retrieved from Limb Global Survey Observations
Swath Objects H2O O3 CH4 CO NO2 HNO3 AtmT
Limb 1 X X X X   X X
Limb 2 X X   X X   X
Limb 3 X X   X X   X

The routine operating procedure for the TES is to make continual sets of nadir and limb observations (plus calibrations) on a 1-day-on, 1-day-off cycle. During the off days, extensive calibrations and special product observations are made. An overview of the acquisition process for global survey is shown bellow. The lower part shows how this process is divided into 81.9-second sequences of calibration, nadir and limb observations. The timing is based on the need for the sampling density to be commensurate with the approximately 5° latitude grid of current chemical-dynamic atmospheric models. Furthermore, acquisition is triggered by the crossing of the southernmost point in the orbit (the southern apex). Thus observations are made at the same latitudes during every orbit, and on every 16th day identical locations are sampled. See the Orbit & Coverage page for more details on the global coverage during a typical day of a TES global survey.

Global Survey Observation Strategy (click to enlarge)

(click to enlarge)