This document is part the Satellite Imagery FAQ
Satellite Imagery
------------------------------
Subject: Weather Satellites
I know nothing about these: need to find some info.
The Meteosat GOES amd GMS weather satellites operate in geostationary orbits.
That is to say, they orbit the Earth at the same speed as the Earth's
rotation, thus constantly viewing the same area. This means that their
temporal resolution is effectively unlimited, so they are able to generate
the familiar weather 'movies'.
They are, however, of limited use for (other) remote sensing purposes.
Geostationary orbits (more typical of communications satellites) are
constrained to high altitude, and to the equator. Thus good viewing
angles over high latitudes are not possible. The very large area images
are at low spatial resolution; the best achieved by Meteosat and GOES
is 2.4Km (?).
Here are a few pointers to weather
pictures online, or see the
Meteorology Resources FAQ for a far longer
list.
------------------------------
Subject: Earth Observation Satellites (for geosciences, etc)
See also the list below, containing pointers to detailed information
and online imagery.
Earth Observation imagery takes a number of forms, of which the most
traditional are optical and near-infrared radiation, from about 0.4 (blue)
to 2.0 (IR) micrometers. Examples include Landsat, Spot and NOAA.
These generally use tracking instrunents, the basic principles of which
are briefly described in Part 2 of this FAQ (someone point me to a
proper intro on the net - SURELY there must be one)!.
Colour
After basic processing, imagery from these satellites may appear as
photographs. With certain visual imagery - eg SPOT - it is even possible to
display images in more-or-less their natural colour. In practice, images for
display are generally manipulated to appear visually pleasing and to show
interesting detail, and appear in false colour. Visible and non-visible
(IR) bands may be freely mixed in false colour images. There are no firm rules
about this, but by convention clouds are shown as white, and vegetation red or
green, depending on the context.
Resolution
Resolution is determined primarily by instrument design, and generally
involves various compromises:
- High spatial resolution implies imaging a small area. For an image of
1000 pixels square, at 20m resolution the area viewed is 20x20Km, but at 1Km
resolution this increases to 1000x1000Km (actually rather more, due to the
variation in viewing angle over a large area). The latter is therefore
intrinsically suited to large-scale studies.
- High spatial resolution also implies a high sampling frequency, which
may limit the sensitivity of the sensor.
Types of Imagery
Apart from visual and near-infrared, other bands of the spectrum commonly
used include thermal infrared (heat) and microwave (radar). Each of these
has its own applications.
3-dimensional Imagery
We see the world in three dimensions by virtue of having two eyes, viewing
the world at slightly different angles. It is possible to emulate this
and produce 3-dimensional (stereo) satellite imagery, by superimposing
images of the same ground area, viewed from different angles (and at
different times). A limited number of satellites have this capability.
------------------------------
Subject: Synthetic Aperture Radar (SAR)
Synthetic Aperture Radar. An active microwave instrument, producing
high-resolution imagery of the Earth's surface in all weather.
There is a good introduction to imaging radar by Tony Freeman of JPL at
http://southport.jpl.nasa.gov/desc/imagingradarv3.html
Should we have an embedded intro for the benefit of non-WWW readers?
I can ask to include the above, or try and solicit an equally expert
intro from someone here
Several past, present and future Earth Observation Satellites. Also the
Shuttle Imaging Radar missions. See the table for a full list.
the future...
- ENVISAT (I'm not even making a link until I've something REAL to put
there)!
- OK, what have I forgotten about (or never heard of)?
Two main properties distinguish SAR from optical imagery:
- The SAR is an active instrument. That is to say, it generates its own
illumination of the scene to be viewed, in the manner of a camera with flash.
The satellite's illumination is coherent: i.e. all the light in any flash is
exactly in phase, in the manner of a laser, so it does not simply disperse
over the distance between the satellite and the Earth's surface.
A SAR instrument can measure both intensity and phase of the reflected
light, resulting not only in a high sensitivity to texture,
but also in some three-dimensional capabilities. Experiments with the
technique of Interferometry (measuring phase differences in
exactly aligned images of the same ground area) have shown that SAR
can accurately model relief, and appears able also to detect small
changes over time.
Some consequences of being an active instrument (and using coherent light) are:
- Works equally day or night
- Polarised - can be used to gain additional information (esp. when
different polarisations are available on the same platform - as on
the most recent Shuttle missions).
- Needs a lot more power than passive sensors, and can therefore only
operate intermittently.
- Suffers from speckle, an artifact of interference patterns in coherent
light, sensitive to texture.
- SAR is Radar - i.e. it uses microwave frequency radiation.
(note that in consequence, references to "light" above should
more strictly read "microwave radiation").
Microwave radiation penetrates cloud and haze, so SAR views the Earth's
surface (land and sea) in all weather. For general purpose Remote Sensing,
this is probably the major advantage of SAR.
An example of its use is the ESA/Eurimage "Earthwatch" programme, producing
imagery of natural and other disasters when weather conditions prevent other
forms of surveillence. Earthwatch imagery is available at
http://gds.esrin.esa.it/CSacquisitions
- Sensitive to texture: good for vegetation studies.
- Ocean waves, winds, currents.
- Seismic Activity
- Moisture content
A list of SAR applications is available at
http://southport.jpl.nasa.gov/science/SAR_REFS.html
Of course, all SAR image colour is false colour: the notion of true colour
is meaningless in the context of invisible microwave radiation.
Most SAR images are monochrome. However, multiple images of the same scene
taken at different times may be superimposed, to generate false-colour
multitemporal images. Colour in these images signifies changes in the scene,
which may arise due to a whole host of factors, such as moisture content or
crop growth on land, or wind and wave conditions at sea. SAR is
particularly well-suited to this technique, due to the absence of cloud cover.
The shuttle SAR's images are the nearest to 'natural' colour, in the sense
that they are viewing three different wavelengths, which can be mapped to
RGB for pseudo-naturalistic display purposes (essentially the same as false
colour in optical/IR imagery).
Need a proper multitemporal image entry
Technique used extensively to map the oceans.
There are introductions at
http://www.satobsys.co.uk/ and
http://dutlru8.lr.tudelft.nl/altim/. The latter includes
the Altimetry Atlas, computed from GEOSAT, ERS-1 and TOPEX-Poseidon
altimetry data.
An interactive browser offering sea surface height maps is available at
http://www.ccar.colorado.edu/~hendricj/topexssh.html
------------------------------
Subject: List of some Earth Observation Satellites
Here is a list of some EO missions. These entries should become
html links to further information (esp. details of imagery and where to get it
if applicable) on an ad-hoc basis, as and when
I have the information to put there (contributions sought)
and the time to edit them in.
For detail on any of the following (and others), try a keyword search
on Esrin's GDS at
http://gds.esrin.esa.it/.
See also
http://gds.esrin.esa.it/CIDN_PROVA.source
- ADEOS Advanced Earth Observing Satellite
- OCTS Ocean Color and Temperature Scanner
- AVNIR Advanced Visible and Near-Infrared Radiometer
- NSCAT NASA Scatterometer
- TOMS Total Ozone Mapping Spectrometer
- POLDER Polarization and Directionality of the Earth's Reflectance
- IMG Interferometric Monitor for Greenhouse Gasses
- ILAS Improved Limb Atmospheric Spectrometer
- RIS Retroflector in Space
- Almaz
- DMSP Defense Meterological Satellite Program
- SSM/I (Special Sensor Microwave/Imager)
- Visible
- SSM/T1, SSM/T2 Microwave temperature & moisture sounders
- ERS-1 Earth Resources Satellite
- AMI (Active Microwave Instrument), Wind mode, Wave mode, SAR
(Synthetic Aperture Radar)
- Radar Altimeter
- ATSR-M (Along-Track Scanning Radiometer and Microwave
Sounder)
- PRARE (Precise Range & Range Rate Equipment)
- ERS-2 as ERS1 with addition of
- GOME Global Ozone Monitoring Experiment
- GEOS Geodynamics Experimental Ocean Satellite
- GEOSAT GEOdetic SATellite
- GMS Geostationary Meteorological Satellites (140 E)
- VISSR (Visible and Infra-red Spin Scan Radiometer)
- GOES Geostationary Operational Environmental Satellite (75 W and 135 W)
- VISSR (Visible and Infra-red Spin Scan Radiometer) altimeter
- HCMM Heat Capacity Mapping Mission
- HCMR (Heat Capacity Mapping Radiometer), visible + thermal
- INSAT Geostationary satellite of India (74 E)
- IRS Indian Remote Sensing Satellite System
- PAN - Panchromatic Camera
- LISS I - III (Linear Imaging Self Scanning Sensors)
- WIFS
- JERS-1 Japanese Earth Resources
Satellite
- OPS Optical Sensors
- SAR (Synthetic Aperture Radar)
- KOSMOS Russian EO satellite
- Landsat
- TM (Thematic Mapper)
- MSS (Multi-Spectral Scanner System)
- RBV (Return Beam Vidicon) camera
- METEOR Russian meteo satellites (2-21, 3-3, 3-5)
- Meteosat (0 E, Greenwich meridian)
- Visible/near infra-red
- middle IR
- Watervapour, thermal infra-red
- MOS Marine Observation Satellite
- MESSR Multispectral Electronic Self Scanning Radiometer
- VTIR Visible and Thermal Infrared Radiometer
- MSR Microwave Scanning Radiometer
- Nimbus 7
- CZCS Coastal Zone Color Scanner
- ERB Earth Radiation Budget
- LIMS Limb Infra-red Monitor for the Stratosphere
- SAM-II Stratospheric Aerosol measurement (II)
- SAMS Stratospheric and Mesospheric Sounder
- SBUV Solar and Backscatter ultraviolet Spectrometer
- TOMS (Total Ozone Mapping Spectrometer)
- SMMR (Scanning Multichannel Microwave Radiometer)
- THIR Temperature Humidity Infra-red Radiometer
- NOAA Polar Orbiting Environmental Satellites
(series)
- AVHRR Advanced Very High Resolution Radiometer
- TOVS (TIROS Operational Vertical Sounder)
- SBUV/2 Solar Backscatter Ultraviolet Spectrometer
- Radarsat (Canada)
- RESURS
- MSU-E High resolution optical scanner
- MSU-SK Medium-resolution Optical-IR
- SeaStar
- SeaWiFS Sea-viewing Wide Field-of-view Sensor
- SeaSat Ocean Dynamics Satellite
- SAR L-band
- ALT Radar altimeter
- SASS Radar Scatterometer
- SMMR Scanning Multi-Spectral Microwave Radiometer
- VIRR Visible en Infra-red Radiometer
- Shuttle
- SIR-A Shuttle Imaging Radar
- SIR-B
- SIR-C (cross polarized returns VH and HV) (Apr+Oct 1994)
- LFC Large Format Camera
- MOMS Modular Opto-electronic Multi-spectral Scanner (2 bands)
- SkyLab
- S 192 MSS Multispectral Scanner
- Metric camera experiment
- SPOT
- HRV High Resolution Visible (2x) has 2 modes:
- XS (MultiSpectral mode)
- PAN (PANchromatic mode)
- SPOT 4 (launch 1995)
- HRVIR High Resolution Visible and Infrared
- TIROS, TOS and ITOS forerunners of the current NOAA series (9-12+14, 13
failed just after launch). See NOAA above.
- AVHRR Advanced Very High Resolution Radiometer
- TOVS (TIROS Operational Vertical Sounder) consisting of:
- HIRS/2 infra-red sounder
- SSU stratospheric sounding unit
- MSU microwave sounding unit
- TOPEX/POSEIDON
- ALT Radar Altimeter
- TMR TOPEX Microwave Radiometer
- LRA Laser Retroreflector Array
- SSALT Single-Frequency Solid-State Radar Altimeter
- DORIS Dual-Doppler Tracking System Receiver
- GPSDR GPS Demonstration Receiver
- TRMM Tropical Rainfall Measuring Mission
(launch 1997, Japan)
- PR Precipitation Radar
- TMI TRMM Microwave Imager
- VIRS Visible Infrared Scanner
- CERES Clouds and the Earth's Radiant Energy System
- LIS Lightning Imaging Sensor
------------------------------
Subject: Military / Intelligence Imagery
FAS (Federation of American Scientists) have compiled a comprehensive
guide to imaging intelligence [IMINT] at
http://www.fas.org/irp/wwwimint.html.
Didn't President Clinton recently declassify some military imagery?
By an order dated 23rd Feb 1995,
- Imagery from the CORONA, ARGON, and LANYARD missions to be declassified
within 18 months.
- Review process to be instituted for other imagery.
Details and imagery are available at
http://edcwww.cr.usgs.gov/dclass/dclass.html.
------------------------------
Subject: Russian Imagery
Contributed by W. Steven Sklaris (then of DBA systems; now
ssklaris@tds.com). Information regarding suppliers and availability applies
to the USA; elsewhere YMMV.
The Russian Federation through the Russian Space Agency permits the sale of
commercial multi-source satellite imagery. The current restriction placed on
this imagery is limited to 2 meter resolution but 1 meter resolutions are
currently being considered. The majority of commercial sources are from film
return systems. The technical philosophy is that the highest quality ground
resolve is acquired by film systems - no argument. The two primary
commercial satellites are KOSMOS, RESURS and Okean. The KOSMOS is utilized
by the ministry of Defense. RESURS and Okean satisfies environmental and
weather monitoring.
The KOSMOS has on board 2 camera systems; the KVR-1000 and TK-350. The main
attraction of the system is for mapping applications. The TK-350 is a frame
camera that provides 80% overlap between images (every third image provides
60%), along with internal and external orientation data. This system
provides for accurate determination of latitude, longitude and elevation.
The TK-350 covers an approximately 265 x 170 kilometer area per image and an
8 to 10 meter resolution. The ground feature characteristics are provided by
the KVR-1000 camera. This camera system operates simultaneously with the TK-
350 and provides 10% overlap between images. This is a panoramic camera with
2 meter ground resolution and 36 - 44 x 165 kilometer area.
The RESURS-O consists of the 01 and 02 series and are direct digital return
systems.
The RESURS-01 has on-board 2 sensor systems; the MSU-E and MSU-SK. The MSU-E
is a three channel system covering the 500 to 900 nanometer band range. The
sensor has a resolution of 45 meters and covers a 45 kilometer swath. The
MSU-SK has 5 distinct channels covering the 540 to 11,800 nanometer band
range. This sensor has a resolution of 160 meters for the first 4 channels
and 600 meters for the 5th channel and covers a 600 kilometer swath.
The RESURS-02 is an upgraded version of the 01 and has 4 on-board sensor
systems; the MSU-E, MSU-SK, SLR "Travers-1T" and MW-radiometer "Delta-2."
The MSU-E on this more recent satellite system covers the same 3 channels as
that of the 01 but the resolution has improved to 25 to 30 meters while
retaining the 45 kilometer swath. The MSU-SK is again included on the RESURS-
02 with no improvement from the 01 version. The Synthetic Aperture Radar
"Travers-1T" and Micro Wave radiometer "Delta-2" operate at a radiation wave
length of 23cm. The Travers-1T has a ground resolve of 200 x 200 meters and
a swath width of 100 kilometers. The Delta-2 has a ground resolve of 17,000
x 90,000 meters and a swath width of 1,000 kilometers.
The RESURS-F consists of the F1, F2 and F3 series.
The RESURS-F1 is the oldest and has on-board 2 camera types; the KATE-200 and
KFA-1000. The KATE-200 is a frame camera with a ground resolution of 15 to
30 meters and covers a ground area of 240 x 240 kilometers. The camera
system has three separate film bands covering 500 to 850 nanometers. The KFA-
1000 is an excellent higher resolution color spectrazonal film camera and
coverage of 80 x 80 kilometers. The resolution advertised is 6 to 8 meters
but is more around 8 to 10 meters. The color spectrazonal film covers the
570 to 680 nanometer and 680 to 810 nanometer band ranges.
The RESURS-F2 is a more sophisiticated topographic camera system. The MK-4
is a true multi-spectral camera system with data recorded on three separate
black and white film bases. There are 6 available bands (460 to 900
nanometers) from which 3 can be selected for imaging. The resolution of the
MK-4 is about 6 to 8 meters and advertised to be excellent for cartographic,
environmental and geological surveys. The coverage of the MK-4 is 150 x 150
kilometers. The RESURS-F2 has on-board 2 stellar cameras to augment
orientation accuracy information but in almost all cases the cameras are not
operated. Because of this the cartographic capabilties are limited without
ground control. The excellent features of the camera are in the resolution
and separate band characteristics.
The RESURS-F3 is the most recent system and the most impressive. The
panchromatic frame camera covers 30 x 30 kilometers with at least 2 meter
resolution. The 1:70,000 to 1:90,000 scale of the imagery provides excellent
ground definition.
The Okean-O is also a digital data return system and known to operate for
ocean monitoring. This satellite has on-board 6 sensor systems; the MSU-V,
MSU-SK, MSU-M, SLR, Scanning MW-radiometer "Delta-2", Track MW-radiometer R-
600 and the Track VW-radiometer. The MSU-V is a eight channel system, the
spectral range is unknown. This sensor has a resolution of 50 meters in the
first 4 channels, 100 meters in the 6th channel and 275 meters in the 7th and
8th channels and covers a 180 to 200 kilometer swath The MSU-SK has 5
distinct channels covering the 540 to 11,800 nanometer band range. This
sensor has a resolution of 160 meters for the first 4 channels and 600 meters
for the 5th channel and covers a 600 kilometer swath. The MSU-M is a four
channel system, the spectral range is unknown. The sensor has a resolution
of 1,600 to 2,000 meters and covers a 1,900 kilometer swath. The Side
Looking Radar operates at a radiation wavelength of 3.1cm at a ground
resolution of 800 to 1,500 meters and a swath width of 450 kilometers. The
Scanning Microwave radiometer "Delta-2" can operate at a wavelength of 0.,8,
1.35, 2.2 or 4.5cm. The resolution is from 20,000 to 100,000 meters and
covers a 800 kilometer swathwidth. The Track Microwave radiometer R-600
operates at a wavelength of 6cm and has a resolution of 130 meters (swath
width unknown). The Track VW-radiometer operates at a wavelength of 2.25 cm
and also has a resolution of 130 meters (swath width unknown).
Numerous problems have been encountered with purchasing satellite source from
Russia. Most of the problems stemmed from the unauthorized source
distributors. Most distributors had access to the archives and conducted a 1
or 2 time sale before they got caught. The Russian Space Agency is now
controling this distribution activity and has eliminated this problem.
Several other problems still exist and will not be resolved in the near
future. Access to coverage in a timely manner is one. The archives of the
KOSMOS system are not catalogued in a digital form and acquiring coverage
information is extensive and timely. Information on coverage is typically
provided in a week (depending on the extent of coverage requested). The
cloud cover information provided with the coverage plots are very accurate
but does not satisfy all users. Several distributors of the TK-350 are
preparing digitization and browsing of the archived image files. Core
Software is considered to be the furthest along in this venture. A digital
database of the RESURS-F exists and provides extensive information relating
to coverage and collection detail. DBA Systems has a copy of this database
in their Melbourne, Florida office and can provide quick turn-around
information. The time to acquire the imagery has been another problem area.
This is much improved and is dependent on the amount of coverage requested.
A single image request, once selected from the coverage plot, will take
approximately 5 to 7 work days. Part of this delay is due to the shipping
services (DHL is 3 days from Moscow). Film quality has also been questioned
and although the processing has significantly improved, many of the archived
images are scratched and were poorly processed during original production.
Several distributors now provide the film sources in digital form. EOSAT and
DBA Systems both can perform digitization of the KVR-1000 down to the 45m
range but only DBA can provide a continuous scan of the entire TK-350 image
down to the 45m spot size if desired (125m is recommended). The precise
scanning of their custom build scanner retains the metric accuracy of the
frame image. Any of the RESURS-F films can also be scanned by the DBA
scanner and JEBCO has also provided digital product from the RESURS-F
archives but we are unsure whether the JEBCO source is still available. The
color spectrazonal film of the KFA-1000 cannot currently be captured by the
DBA scanner and other providers of color scanning of the KFA-1000 are unknown.
There are several suppliers of Russian imagery and value-added products
created from the various Russian satellite systems. EOSAT, through
authorized Russian distributor Kieberso, provides digital KVR-1000; Core
Software through authorized Russian distributor SOVINFORMSPUTNIK, provides
hardcopy and digital KVR-1000 and TK-350; DBA Systems through multiple
authorized Russian distributors of KOSMOS, RESURS and ALMAZ, provides the
majority of Russian satellite sources in both hardcopy and digital form.
Yes, the RESURS-F1M and RESURS-F2M will be upgrades to the existing film
return systems and a newer system referred to as Nika-Kuban will be added to
the RESURS satellite family. The Nika-Kuban will operate 3 camera systems
and 1 forward looking digital return system to assist in eliminating
collection of cloud covered imagery. The Nika-Kuban will offer panchromatic
and multispectral collection in the 3 to 6 meter resolution range. Also
planned as a major player in the commercial remote sensing industry will be
the ALMAZ-1B and ALMAZ-1C. Both systems are currently awaiting financing to
complete development but will house the most sophisticated array of remote
sensing systems available in the commercial market. The ALMAZ-1B will offer
a unique, complex, multi-sensor payload providing for the first time, a
capability for simultaneous, multi-sensor, high resolution imagery, including
single-pass stereo coverage in the optical and multispectral bandwidths; and
high resolution, two-pass, all weather stereo in microwave bandwidths.
Russian Imagery section by
W. Steven Sklaris
DBA Systems, Inc.
1200 South Woody Burke Rd.
Melbourne, Florida 32901
ph: 1-800-622-8554
fax: (407) 727-7019
------------------------------
Subject: Where can I get Imagery?
This very frequently asked question has several parts, which are
addressed in various parts of this FAQ:
------------------------------
Subject: How do I access the imagery catalogues?
There are a number of catalogue services available for interactive login, via
telnet; a few of these also offer alternative access methods, including WWW.
These will give full catalogue information, and browse products online
(typically by ftp).
Some addresses for these are listed under
further reading.
CEOS IDN
The CEOS International Directory Network comprises three coordinating nodes,
together with a number of cooperating nodes. Each coordinating node
includes access to every known imagery catalogue, so in principle you never
need more than one address. These are listed in
further information.
Cintex
The Catalogue Interoperability Experiment aims to ensure interoperability
between the various catalogues.
GUIs for catalogue access
Various dedicated GUI systems exist to assist CINTEX catalogue users.
These include:
- DLR ISIS
- ESA UIT
- NASA EOSDIS V0 IMS
Details are available at
http://gds.esrin.esa.it/Ccintex.cs.clients.
WWW Browse Services
In addition to the login services, there are some services available on the WWW,
offering a world-map and forms-based interface. These include:
- http://shark1.esrin.esa.it/
- Ionia AVHRR browser
- http://tracy.esrin.esa.it:8001/
- Eye-Browser Multi-Mission Browse Service: NOAA AVHRR, ERS-1 SAR,
JERS OPS, Landsat TM.
- http://www.coresw.com
- "Imagenet" service - Landsat, SPOT and a promise of Sovinformsputnik.
Appears only to have data for America when last checked. Commercial;
the free service is limited.
-
http://www.eurimage.it/einet/einet_home.html
- EiNet (European Imagenet) from Eurimage offers Landsat TM, KVR-1000 and
RESURS.
- http://southport.jpl.nasa.gov/general.html/
- SIR-C/X-SAR (Space Shuttle) imagery.
-
http://ic-www.arc.nasa.gov/ic/projects/bayes-group/Atlas/Earth/
- Browser for Earth Observations from Shuttle
------------------------------
Subject: Where can I get full-resolution imagery cheap or free?
Answer 1: In general, you can't!
Answer 2: Old Landsat. The following was posted by Wim Bakker on IMAGRS-L:
Paul DeVries (bosse@bahnhof.se) writes:
> Can anyone point me in the direction of satellite imagery of (dry) Andean
> altiplano, very cheap or in the public domain, of any vintage? Thanks.
In principle the old Landsat TM (acquired from July 16, 1982 through
September 27, 1985) and old Landsat MSS (older than 2 year) are
available at reduced prices:
MSS $ 200
TM raw $ 300
TM systematic corrected $ 425
TM precision corrected $ 600
Inquires can be made to
Customer Services
EROS Data Center (EDC)
Sioux Falls SD 57198
(605)-594-6151
In the mean time you can check on the Inventory service of EDC
URL telnet://glis.cr.usgs.gov
whether any images of your area of interest are available.
Wim Bakker's report "Remote Sensing Data and GIS data on CD-ROM"
is available at
http://www.itc.nl/~bakker/info/rs-data/index.html
Note - this is referenced for want of a better list, but is not kept
up-to-date.
------------------------------
Subject: Whole-World Images
This answer is slanted towards Global AVHRR Land datasets. Anyone
care to talk about other images?
- Why create whole-world images?
- Because they're fun, of course! :-)
Continental to global scale images are useful if they show information
that is studied at a large scale, such as the state of the global biosphere.
One major measure is NDVI, which characterises 'greenness' (see
RS/Vegetation FAQ for details). Global NDVI
images taken regularly over time - at intervals between one and two weeks -
enable scientists to study change in the biosphere in detail.
- How do they create whole-world images
- The AVHRR Pathfinder and Global 1KM projects have created global land
datasets showing NDVI (together with lower-level data) from AVHRR
imagery, at resolutions up to 1.1KM. The global images are created by
mosaicing a large number of individual scenes, taken over ten-day periods.
Individual scenes are first stitched to generate half-orbits (in principle
south to north pole, but generally broken because only daytime data is used)!
The half orbits are then
stitched together, with reference to a digital chart of the world.
The key to compositing for NDVI is that each point on the Earth's surface
is replicated in several images over the sampling period. Only the
best NDVI value is selected, so bad data (such as cloud cover)
is discarded.
- Why AVHRR? Why not, say, Landsat?
-
Yes, Landsat data is just as well-suited to computing NDVI as is the AVHRR.
The NOAA satellites, in a polar orbit at an altitude of 833 KM, orbit the
Earth fourteen times per day. The AVHRR instrument images a 2400-KM wide
swath as it passes. Thus every point on the Earth's surface is viewed
at least about once per day (the exact frequency of course varies with
latitude).
The Landsat series (4-5), in near-polar orbits at 705 KM, also orbit the
Earth fourteen times per day. However, the swath imaged is just 185KM,
so a point on the equator may be viewed only once in sixteen days.
The data with which to generate weekly, ten-day or fortnightly global
composites is simply not available. A sixteen-day composite would
of course be subject to considerable cloud-cover (see below).
Having said that, it is certainly possible to make large-area Landsat
mosaics. NASA's Landsat Pathfinder Project (see
http://pathfinder-www.sr.unh.edu/pathfinder/) has created such
datasets for the study of tropical deforestation.
- How do they get rid of the cloud?
- As noted above, only the best NDVI values from each input dataset is used.
Clouds will necessarily generate very low NDVI values - clouds are not
green!. Hence clouds are automatically filtered out in the compositing
process, provided there is at least one cloudless view of a point within the
sample. Thus cloudlessness is not in fact guaranteed, but is statistically far
more likely than for a single pass. Alternatively, it can be assured by
collecting data over an unlimited time period; c.f. the GeoSphere project).
Clearly this will work if and only if the characteristics being studied
are dissimilar to any cloud in at least one of the available bands!
Further reading:
-
http://sun1.cr.usgs.gov/landdaac/1KM/1kmhomepage.html
- Global Land 1-KM Project Front Page from USGS/EDC. Includes
extensive description of the project, and access to the data.
- http://atlas.esrin.esa.it:8000/
- Global AVHRR 1KM Server from ESA/ESRIN. The contents is essentially
the same as the EDC server; readers should normally use whichever is closer
to you in terms of Net connections.
- http://shark1.esrin.esa.it/
- Ionia browser - AVHRR scenes and a browse version of a
global composite from ESA/ESRIN
-
http://xtreme.gsfc.nasa.gov/
- AVHRR Land Pathfinder from NASA/GSFC - various global composites.
-
http://infolane.com/infolane/geosphere/geospher.html
- The GeoSphere project (commercial)
All the above references deal with global land datasets. NASA's pathfinder
program created also Ocean and Atmospheric datasets:
- http://sst-www.jpl.nasa.gov/
- SST Pathfinder from NASA/JPL
- http://pegasus.nesdis.noaa.gov/pathfinder.html
- Atmosphere pathfinder from NOAA
General Questions
------------------------------
Subject: Programmes and Policies
(Should I have a brief summary and/or plain list here?
This is dealt with in detail in a US Congress (Office of Technology
Assessment) report "Remotely Sensed Data: Technology, Management and Markets",
Chapter 5. Whilst this *is* explicitly a US government document, it is
generally an objective summary!
The report is available online at
http://otabbs.ota.gov/T90 (thanks to Mark_Goodman@achre.gov for
drawing my attention to the OTA reports).
USA: See also the previous question.
The US Congress (Office of Technology Assessment) has published
some detailed reports, two of which are available online. In addition to
the report referenced in the previous question above,
"Civilian Satellite Remote Sensing: A Strategic Approach" is available at
http://otabbs.ota.gov/T85.
Others: AFAIK no such government documents are available elsewhere (but
see CEOS below for worldwide policy coordination). Check the various
space agency pages, listed under URLS.
------------------------------
Subject: Where can I find information on RS and the Environment
This is far too big a subject to cover in this FAQ, so here are some links,
limited to major (and established) collections:
- Environmental Resources Information Network, ERIN (Australia)
-
- The ERIN homepage is at
http://kaos.erin.gov.au/erin.html (formerly listed under misc. URLS)
- Global Environmental Research Federal Metadata Network GENIE
- at http://www-genie.lut.ac.uk/.
- United States Geological Survey - Environment
- http://www.usgs.gov/environment/index.html
- United Nations Environment Programme
- Frontpage is at href=http://www.unep.ch.
The main RS/GIS related information is in the
Global Resource Information Database (GRID) at sites including
http://www.grid.unep.ch/gridhome.html,
http://www.grida.no/ and
http://www.inpe.br/grid/home
- US Global Change Research Information Office (GCRIO)
- http://www.gcrio.org/
------------------------------
Subject: Using imagery during Natural (and other) disasters.
Earthquakes, floods, volcanos, mega-icebergs, pollution disasters...
There is imagery for all of them! Watch relevant newsgroups as news of
a disaster breaks.
That's not to say there is immediate and extensive coverage of every possible
event: the satellites capable of imaging it may not be in the right place
at the right time! However, systematic programmes exist; notably the
ESA/Eurimage Earthwatch program at
http://www.eurimage.it/Earth_Watching/Earth_Watching.html
(formerly listed at
http://gds.esrin.esa.it/CSacquisitions
which is still valid)
------------------------------
Subject: Jobs
Note: there is a very high percentage of duplication between
these sources!
In addition to the above,
comp.infosystems.gis tolerates a certain range of job postings.
Please read the detailed guidelines in that group's FAQ before posting.
------------------------------
Subject: Online Services Exchanges / Trade Fairs
The following interactive web sites are perhaps best described as
'trade fairs':
A similar but non-interactive site is
------------------------------
Subject: Geoscience Journal Information
The UCSD service referenced in the August96 update of the SATFAQ drew
quite a lot of error reports, and has been withdrawn from here.
Elsevier have a mail server offering the tables of contents of their
Earth and Planetary Science journals. The subscription address for
all titles is earth-e@elsevier.nl.
For information on the service, use subject line "help".
A good reference point on the Web is Bill Corner's site, at
http://www.man.ac.uk/Arts/geography/rs/rs_journal.html.
------------------------------
Subject: Software + hardware
Here's a complete cop-out: software is rather well covered in related
documents.
There is an excellect collection of reviews,
now maintained by Vinton Valentine at
http://triton.cms.udel.edu:80/~oliver/gis_gip/gis_gip_list.html.
In spite of the "gislist" name, this deals extensively with Remote Sensing
and Image Processing software. Furthermore, comments and reviews are
generally independent of the manufacturers/distributors.
Where can I find information on Software Packages?
These questions are covered in the comp.infosystems.gis FAQ and the "Using
the Web for Geoscience Resources" FAQ, among others.
See the Public Domain Cartographic Software FAQ.
Pointers to the FAQs are here.
Free packages for image processing include:
A few more listed FYI with no comment (in all but one case, simply because
I know nothing):
This question is dealt with in detail in the WXSAT FAQ and other documents at
ftp://kestrel.umd.edu/pub/wxsat/docs/.
There is a nice "Build your own HRPT groundstation" webpage at
http://www.msoft.it/noaa95/.
------------------------------
Subject: Standards
Committee on Earth Observations Satellites (CEOS)
I hope reproducing this paragraph isn't violating copyright - anyone?
It comes from too many sources to attribute!
CEOS was created in 1984 as a result of the international Economic Summit
of Industrialized Nations and serves as the focal point for international
coordination of space-related, Earth observation activities. Policy and
technical issues of common interest related to the whole spectrum of
Earth observation satellite missions and data received from such are
addressed. CEOS encourages complementarity and compatibility among space-borne
Earth observing systems through coordination in mission planning,
promotion of full and non-discriminatory data access, setting of data
product standards, and development of compatible data products, services,
and applications. The user community benefits directly from this
international coordination.
The CEOS information system is at
http://gds.esrin.esa.it/CCEOSinfo, and contains full details and
CEOS files.
See also CEOS calibration pages at
http://southport.jpl.nasa.gov/calceos/calceos.html
CEOS also sponsors
The CEOS International Directory Network (CEOS IDN)
Need someone to wirte a real entry
This is the authoritative worldwide information system that answers every
possible question about Satellite Earth Observation. The complete
database is held at the three coordinating nodes in America (NASA/GSFC),
Europe (ESA/ESRIN) and Asia (NASDA/EOC). For access details, see under
Further Information.
------------------------------
Subject: Copyright
Wim Bakker recently supplied the following article, in part a translation
from a (Dutch) NLR article. I have taken the liberty of cutting it down
somewhat.
I understand the issue of copyright on satellite imagery may in fact
vary significantly depending on what country you're in. Mark Goodman
(Mark_Goodman@achre.gov) writing from a US point of view comments:
I'm not sure that satellite imagery is covered by copyright law.
It may depend on what country you're in. I believe that SPOT and
EOSAT protect their intellectual property rights through trade
secrets laws, and through restrictive sales contracts that prohibit
redistribution of raw data, even for scientific use!
Your mileage may vary!
© Copyright
There is a lot of confusion about the copyright connected to the use of
satellite images and everything related to this.
According to Websters dictionary "copyright" is
copy.right \-.r{i-}t\ n : the exclusive legal right to reproduce,
publish, and sell the matter and form of a literary, musical, or artistic
work - copyright aj
- copyright vt : to secure a copyright on
In 1886, during the Convention of Bern the matter of copyright was
regulated internationally. It states that the author (creator) of a certain
matter remains the owner of his product. This also means that if you
buy a copyrighted product you pay for the use of this product and
you can never claim to be the owner of such a product. Furthermore, you
can never claim any other rights about such a product (e.g. the right
to reproduce the product).
In copyright the following 5 stages can be distinguished:
- the creation of a product
- the manufacturing of a product
- the distribution of a product
- the use of a product
- the reproduction of a product
These 5 points can also be distinguished with the use of satellite images.
Two operational Earth observing satellites will be described here:
Landsat and
SPOT.
Here I have cut a detailed description of Landsat and SPOT distribution,
as being (IMHO) too detailed for this FAQ - NK.
Now when does the copyright principle touch the user?
Only when the user reproduces or copies (point 5) the satellite images is he
affected by the copyright issue. At all times the user must be aware of
the owner/producer of the data. The owner/producer may or may not permit
the reproduction of the datas, but must in any case
be mentioned on all publications of satellite images!
Note: the following details may vary in different parts of the world,
although the principles apply in any case.
For SPOT data this will be CNES; for Landsat
data received by European ground stations this will be
ESA; and for Landsat data from America
this will be EOSAT (or
NOAA and
EROS Data Center (EDC) for old data).
The owner/producer indicates which reproductions are allowed. The
reproduction of raw data - copying CCT's and film - is never allowed and
for other categories that are allowed the owner will ask for a certain
contribution for the right to reproduce the data; this is called the
reproduction fee.
The following reproductions are free of reproduction fee
- Posters, slides, advertisement or publications used for conferences,
meetings, symposiums and exhibitions in the field of Remote Sensing.
- Technical reports of RS conferences, symposiums etc.
- Scientific reports and papers
For the following, a reproduction fee is due:
- Newspapers
- Magazines
- Brochures
- Books not related to the field of RS
- Posters, either ones that are sold as well as free copies
- Calendars
- Atlasses
- Postcards and invitations
- Using images on TV and video
At all times the owner/producer must be mentioned on the reproductions, even
if no reproduction fee is due!
This can be done in two ways
- To use the word copyright followed by the owner/producer and the
year of production. E.g.
Copyright ESA 1988
- To use the international sign for copyright © followed
by the owner/producer and the year of production. E.g.
© CNES/NLR 1994
In the last example the NLR could have
processed data from
SPOT.
Conclusion
- For some (scientific) applications you owe no reproduction fee.
- At all times the owner/producer must be mentioned on reproductions using
the word copyright or the sign ©
- In case of doubt, ask your distributor!