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Instrument details
Acronym
VAS
Full name
VISSR Atmospheric Sounder
Purpose
Cloud imagery and atmospheric temperature and humidity sounding
Short description
Filter radiometer alternatively used for cloud imagery (2 channels: 0.55-0.75 μm and 10.5-12.6 μm) or atmospheric sounding (12 channels centred on 3.94, 4.44, 4.51, 6.7, 7.2, 11.2, 12.7, 13.3, 14.0, 14.2, 14.5 and 14.7 μm). The required SNR is achieved by selecting appropriate spatial resolution and number of repeated scan lines for the different channels
Background
Implemented by adding absorbing channels to VISSR flown on SMS 1/2 and GOES 1/2/3
Scanning Technique
W-E continuous scanning (100 rps) by the spinning satellite rotation, N-S by mechanical stepping. For sounding channels, for each step the line can be repeated a number of times as required by SNR considerations
Resolution
VIS channel: 0.9 km at s.s.p.; 10.5-12.6 μm channel: 6.9 km at s.s.p.; all other channels: either 6.9 or 13.8 km
Coverage / Cycle
Imaging mode: full disk each 30 min; sounding mode: 400x400 km2 in 20 min; several combinations possible
Mass
74.8 kg
Power
Data Rate
Providing Agency
NOAA
Instrument Maturity
Flown on operational programme
Utilization Period:
1980 to 1988-11-22
Last update:
2014-07-09
Detailed characteristics
Satellites this instrument is flying on
Note: a red tag indicates satellites no longer operational, a
green tag indicates operational satellites, a blue tag indicates
future satellites
Instrument classification
Earth observation instrument Passive optical radiometer or spectrometer Cross-nadir infrared sounder, possibly including VIS channels
WIGOS Subcomponents
No WIGOS subcomponents have been defined.
Mission objectives
Primary mission objectives Atmospheric temperature Integrated Water Vapour (IWV) Specific humidity Secondary mission objectives
Opportunity objectives Cloud top height Cloud top temperature Cloud type Downward long-wave irradiance at Earth surface Land surface temperature Upward long-wave irradiance at Earth surface Upward long-wave irradiance at TOA Show all Show fewer
Tentative Evaluation of Measurements
The following list indicates which measurements can typically be
retrieved from this category of instrument. To see a full Gap Analysis by Variable,
click on the respective variable.
Note: table can be sorted by clicking on the column headers
Variable Relevance for measuring this variable Operational limitations Explanation
Atmospheric temperature 3 - high Cloud sensitive.. Coarse vertical resolution. Several MWIR and TIR channels in the 4.3 and 15 micrometer bands. Frequent sampling (GEO) enables monitoring instability onset
Cloud cover 4 - fair Discontinuous coverage. MWIR and TIR channels
Cloud top height 2 - very high Discontinuous coverage. TIR channels in window and water vapour band (for emissivity) for temperature; and in CO2 band for atmospheric column above cloud top
Cloud top temperature 2 - very high Discontinuous coverage. TIR channels in window and water vapour band (for emissivity)
Cloud type 4 - fair Discontinuous coverage. MWIR and TIR channels
Downward long-wave irradiance at Earth surface 3 - high Cloud sensitive.. Highly indirect. MWIR and TIR channels including water vapour and CO2 bands
Land surface temperature 3 - high Cloud sensitive.. Coarse spatial resolution. MWIR and TIR window channels (high sensitivity to high temperature, cloud impact reduction, water vapour correction)
Sea surface temperature 2 - very high Cloud sensitive. MWIR and TIR window channels (cloud impact reduction, water vapour correction)
Specific humidity 3 - high Cloud sensitive.. Very coarse vertical resolution.. Middle troposphere only. TIR channels in the water vapour band around 6.3 micrometers
Integrated Water Vapour (IWV) 3 - high Cloud sensitive.. Inaccurate in high troposphere. TIR channels around 6.3 micrometers and in the 11 micrometers split window
Upward long-wave irradiance at TOA 4 - fair Spectral interpolation needed. MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in water vapour and CO2 bands around 4,3, 6.3 and 15 micrometers
Upward long-wave irradiance at Earth surface 3 - high Cloud sensitive.. Highly indirect. MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in water vapour and CO2 bands around 4,3, 6.3 and 15 micrometers
Instrument: VAS