GUIDE ON INSTRUMENTS AND METHODS OF OBSERVATION
Part IV : satellite observations
INDEX
1
INTRODUCTION
1.1
1.2
1.3
Historical perspective
Spatial and temporal scale
Complementarity of satellite and ground-based measurements
2.
2.1
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.2
2.2.1
2.2.2
2.2.3
2.2.3.1
2.2.3.2
2.2.3.3
2.2.3.4
2.2.4
2.2.4.1
2.2.4.2
2.2.4.3
2.2.5
2.2.5.1
2.2.5.2
2.2.5.3
2.3
2.3.1
2.3.1.1
2.3.1.2
2.3.1.3
2.3.1.4
2.3.1.5
2.3.1.6
2.3.2
2.3.2.1
2.3.2.2
2.3.2.3
2.3.2.4
2.3.2.5
2.3.2.6
PRINCIPLES OF EARTH OBSERVATION FROM SPACE
Orbits and Earth viewing from space
Satellite and instrument field of views
Orbital period, geostationary orbit, observing cycle, repeat cycle
Orbital precession, sun-synchronous orbits, drifting orbits
Elliptical orbits
Launchers and injection into orbit
Principles of remote sensing
The electromagnetic spectrum utilised for remote sensing
The basic laws of the interaction between e.m. radiation and matter
Observations in the atmospheric windows
Emerging radiation
Measurements in VIS+NIR+SWIR
Measurements in MWIR and TIR
Measurements in MW
Observations in absorption bands
The radiative transfer equation
Profiles retrieval
Limb sounding
Active sensing
Radio occultation
Radar
Lidar
Space and Ground segments
The Space segment
Platform services
Navigation and positioning systems
Orientation and stabilisation
The housekeeping system
Data transmission
Data relay services
The Ground segment
Central station for satellite control and global data acquisition
The mission and operations control centres
The data processing and archiving centres
Data and products distribution
User receiving stations
Product processing levels
3.
3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.2
REMOTE SENSING INSTRUMENTS
Instruments basic characteristics
Scanning, swath, observing cycle
Spectral range: radiometers and spectrometers
Spatial resolution (IFOV, pixel, MTF)
Radiometric resolution
Instrument classification
CIMO Guide, Part IV, Satellite observations - Index
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.2.9
3.2.10
3.2.11
3.2.12
3.2.13
3.2.14
3.2.15
3.2.16
3.2.17
3.2.18
3.2.19
Moderate-resolution optical imagers
High-resolution optical imagers
Cross-nadir scanning short-wave sounders
Cross-nadir scanning infrared sounders
Microwave radiometers
Limb sounders
Broadband radiometers
Solar irradiance monitors
GNSS radio-occultation sounders
Lightning imagers
Cloud and precipitation radar
Radar scatterometers
Radar altimeters
Imaging radar (SAR)
Lidar-based instruments
Gradiometers/accelerometers
Solar activity monitors
Space environment monitors
Magnetometers and electric field sensors
4.
4.1
4.1.1
4.1.2
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.4
4.4.1
4.4.2
4.4.3
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.2
4.6.2.1
4.6.2.2
4.6.2.3
SATELLITE PROGRAMMES
Operational meteorological satellites
Meteorological satellites in geostationary or highly elliptical orbit
Meteorological satellites in sun-synchronous orbit
Specialised atmospheric missions
Precipitation
Radio occultation
Atmospheric radiation
Atmospheric chemistry
Atmospheric dynamics
Missions to ocean and sea-ice
Ocean topography
Ocean colour
Sea surface wind
Sea surface salinity
Waves
Land observation missions
Main operational or near-operational missions
The Disaster Monitoring Constellation
All-weather high-resolution monitoring (by SAR)
Missions to Solid Earth
Space geodesy
Earth’s interior
Missions to Space weather
Solar activity monitoring
Magnetosphere and ionosphere monitoring
Observation of the Magnetosphere
Observation of the Ionosphere
Space environment observation from operational meteorological satellites
5.
5.1
5.1.1
5.1.2
5.1.2.1
5.1.2.2
SPACE-BASED OBSERVATION OF GEOPHYSICAL VARIABLES
Introduction
Processing levels
Products quality
Atmospheric volumes (relevant to profiles)
The horizontal resolution (x)
3
CIMO Guide, Part IV, Satellite observations - Index
5.1.2.3
5.1.2.4
5.1.2.5
5.1.2.6
5.1.3
5.2
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
5.3
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
5.3.6
5.3.7
5.3.8
5.3.9
5.3.10
5.3.11
5.3.12
5.3.13
5.3.14
5.3.15
5.3.16
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.4.6
5.4.7
5.4.8
5.4.9
5.4.10
5.4.11
5.4.12
5.4.13
5.4.14
5.4.15
5.4.16
5.4.17
5.4.18
5.5
5.5.1
5.5.2
5.5.3
5.5.4
5.5.5
5.5.6
The vertical resolution (z)
The observing cycle (t)
The accuracy (RMS)
The timeliness ()
Evaluation of satellite product quality
Basic atmospheric 3D and 2D variables
Atmospheric temperature
Specific humidity
Wind (horizontal)
Wind vector over the surface (horizontal)
Height of the top of the Planetary Boundary Layer
Height of the tropopause
Temperature of the tropopause
Cloud and Precipitation variables
Cloud top temperature
Cloud top height
Cloud type
Cloud cover
Cloud base height
Cloud optical depth
Cloud liquid water
Cloud drop effective radius
Cloud ice
Cloud ice effective radius
Freezing level height in clouds
Melting layer depth in clouds
Precipitation (liquid or solid)
Precipitation intensity at surface (liquid or solid)
Accumulated precipitation (over 24 hours)
Lightning detection
Aerosol and Radiation
Aerosol optical depth
Aerosol concentration
Aerosol effective radius
Aerosol type
Volcanic ash
Downward solar irradiance at TOA
Upward spectral radiance at TOA
Upward long-wave irradiance at TOA
Upward short-wave irradiance at TOA
Short-wave cloud reflectance
Downward LW irradiance at Earth’s surface
Downward SW irradiance at Earth’s surface
Earth’s surface albedo
Earth’s surface SW bi-directional reflectance
Upward long-wave irradiance at Earth’s surface
Long-wave Earth surface emissivity
Photosynthetically Active Radiation (PAR)
Fraction of Absorbed Photosynthetically Active Radiation (FAPAR)
Ocean and sea-ice
Ocean chlorophyll concentration
Colour Dissolved Organic Matter (CDOM)
Ocean suspended sediments concentration
Ocean Diffuse Attenuation Coefficient (DAC)
Oil spill cover
Sea surface temperature
4
CIMO Guide, Part IV, Satellite observations - Index
5.5.7
5.5.8
5.5.9
5.5.10
5.5.11
5.5.12
5.5.13
5.5.14
5.5.15
5.5.16
5.6
5.6.1
5.6.2
5.6.3
5.6.4
5.6.5
5.6.6
5.6.7
5.6.8
5.6.9
5.6.10
5.6.11
5.6.12
5.6.13
5.6.14
5.6.15
5.6.16
5.6.17
5.6.18
5.7
5.7.1
5.7.2
5.7.3
5.7.4
5.7.5
5.8
5.8.1
5.8.2
5.8.3
5.8.4
5.8.5
5.8.6
5.8.7
5.8.8
5.8.9
5.8.10
5.8.11
5.8.12
5.8.13
5.8.14
5.8.15
5.8.16
5.8.17
5.8.18
5.8.19
5.8.20
Sea surface salinity
Ocean dynamic topography
Coastal sea level (tide)
Significant wave height
Dominant wave direction
Dominant wave period
Wave directional energy frequency spectrum
Sea-ice cover
Sea-ice thickness
Sea-ice type
Land surface (including snow)
Land surface temperature
Soil moisture at surface
Soil moisture (in the roots region)
Fraction of vegetated land
Vegetation type
Leaf Area Index (LAI)
Normalised Difference Vegetation Index (NDVI)
Fire fractional cover
Fire temperature
Fire radiative power
Snow status (wet/dry)
Snow cover
Snow water equivalent
Soil type
Land cover
Land surface topography
Glacier cover
Glacier topography
Solid Earth
Geoid
Crustal plates positioning
Crustal motion (horizontal and vertical)
Gravity field
Gravity gradients
Atmospheric chemistry
O3
BrO
C2H2
C2H6
CFC-11
CFC-12
CH2O
CH4
ClO
ClONO2
CO
CO2
COS
H2O
HCl
HDO
HNO3
N2O
N2O5
NO
5
CIMO Guide, Part IV, Satellite observations - Index
5.8.21
NO2
5.8.22
OH
5.8.23
PAN
5.8.24
PSC occurrence
5.8.25
SF6
5.8.26
SO2
5.9
Space Weather
5.9.1
Total Electron Content (TEC)
5.9.2
Electron density
5.9.3
Magnetic field
5.9.4
Electric field
5.9.5
Charged particles
5.9.6
Solar activity
Annex to Chapter 5
6.
6.1
6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
6.1.6
6.1.7
CALIBRATION AND VALIDATION
Instrument calibration
Introduction
Factors affecting calibration
Pre-flight calibration
On-board calibration
Vicarious calibration
Inter-calibration by simultaneous observations
Bias adjustment of long-term data records
6.1.8
6.1.9
6.2
6.2.1
6.2.2
6.2.3
Using calibration information
Traceability of space-based measurement
Product validation
Factors to be accounted for in validation
Validation strategies
Impact studies
7.
7.1
7.1.1
7.1.2
7.1.3
7.1.4
7.2
7.2.1
7.2.2
7.3
7.3.1
7.3.2
7.3.3
CROSS-CUTTING ISSUES
Frequency protection issues
Overall frequency management
Passive MW radiometry
Active MW sensing
Satellite operation and communication frequencies
International coordination
The coordination Group for Meteorological Satellites (CGMS)
The Committee on Earth Observation Satellites (CEOS)
Satellite mission planning
Programme lifecycle
Continuity and contingency planning
Long-term evolution
REFERENCES
ACRONYMS
6
CIMO Guide, Part IV, Satellite observations - 1. Introduction
1.
INTRODUCTION
1.1
Historical perspective
1
On the 1st of April 1960, a new era started for meteorology with the launch of TIROS-1. Weather
systems, which had only been depicted until then by synoptic maps and aircraft observations, could
be visualized at a glance. Their explosive dynamics became more evident with geostationary
imagery from ATS-1 on 6 December 1966. The term “Nowcasting” emerged, as the first application
of meteorological satellites.
Though initial satellite data utilisation was nearly exclusively for Nowcasting, commencing with
Nimbus-3 (13 April 1969), it was first applied to the field of Numerical Weather Prediction (NWP) by
using data from experimental instruments to derive vertical profiles of atmospheric temperature and
humidity and by deriving cloud-motion winds from geostationary image sequences.
The First Global Atmospheric Research Programme (GARP) Global Experiment (FGGE, 1979-80)
was able to assemble, for the first time, a composite system of four geostationary satellites and two
near-polar satellites, which delivered global sounding and imaging coverage four times a day and
imagery at low and mid latitudes half-hourly. It is important to note that since their early days, in
addition to supporting operational applications, meteorological satellites enabled advances to be
made in the understanding of atmospheric dynamics and climate.
Driven by the high economic value of earth resource exploration and vegetation cycle monitoring,
new satellite programmes emerged with a focus on land surface observation. Landsat-1, launched
on 23 July 1972, led the first series of high resolution land observation satellites and coverage from
the SPOT series commenced on 22 February 1986 with SPOT-1, providing imagery at a spatial
resolution of 10 to 20 metres.
Exploration of the Ocean began with the launch of SeaSat on 27 June 1978, which marked the
advent of all-weather microwave sensing, both active and passive. Almost simultaneously, on 24
October 1978, Nimbus-7 pursued microwave passive sensing with the addition of ocean colour
monitoring. After the precursor SeaSat altimetry, scatterometry and SAR imagery missions, no
active sensing mission was operated until the launch of ERS-1 on 17 July 1991. Retrieval of
information on atmospheric radiation and chemistry was initially explored by several Nimbus
missions. A milestone for Earth radiation study was ERBS (5 October 1984). For atmospheric
chemistry a major milestone was UARS (12 September 1991).
1.2
Spatial and temporal scales
The concept of the Global Observing System was totally revised with the advent of satellites, taking
advantage of the complementary nature of ground-based and space-based observations. The
space-based component offers the unique opportunity of uninterrupted global coverage, and
frequent observing cycle. A striking advantage is the capability of atmospheric vertical sounding
over the oceans, alleviating a great limitation of observations for global NWP. Over continental
areas, observing networks are biased towards populated areas, whereas the vast majority of land
surfaces are relatively un-populated, hence under-sampled; furthermore, some local observations
available from the ground (e.g., cloud type) are hard to integrate spatially.
One important difference between satellite and ground measurements is the integration in space
and time. Satellite measurements integrate the incoming signal over an Instantaneous Field Of
View (IFOV) determined by the need to collect sufficient radiant energy to provide the required
Signal-to-Noise Ratio (SNR). Ground measurements are usually point-related, although, depending
on the observed variable, the measurement may be representative of a larger or smaller area. In
the time dimension, the situation is reversed: satellite measurements are nearly instantaneous, due
to the satellite motion or the time available to acquire a picture element (pixel) when scanning an
image; ground measurements usually integrate over a certain time interval in order to average
instantaneous fluctuations. These differences impact on the complexity of comparing or combining
satellite and ground measurements.
1.3
Complementary nature of satellite and ground-based measurements
It is acknowledged that satellites are unable to perform all needed observations with the required
measurement quality. For certain geophysical variables no remote sensing principle exists. For
others, the required measurement quality is only achievable with ancillary information from
accurate ground-based observing systems. In addition, since satellite measurements are often of
indirect nature (the primary observed quantity being radiation), ground measurements play a key
role for the validation of satellite-derived products.
There are still areas where exclusively ground-based systems can provide measurements of
acceptable quality. Even in those cases, satellites can be useful in spatially extending local and
sparse ground measurements. In particular, the practice of assimilation enables transferring
information across geophysical variables measured by means of different techniques: this means
that satellite observations may contribute to the knowledge of geophysical variables even when not
directly observed from satellite, provided that there is a strong physical relationship between these
variables. Synergistic utilisation of ground-based and space-based observations is fundamental to
the WMO Integrated Global Observing Systems (WIGOS).
NOTE: Detailed descriptions of satellite programmes and instruments are available in the WMO
online database of space-based observation capabilities, available from the WMO website:
www.wmo.int/oscar.