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The View from ElsewhereThe Emerging Need for Non-LEO Vantage
Points
The View from ElsewhereThe View from ElsewhereThe Emerging Need for NonThe Emerging Need for Non--LEO Vantage LEO Vantage
PointsPoints
Mark Schoeberl & Peter Hildebrand & Jay HermanNASA, Goddard Space Flight Center
&Carol Raymond
NASA, Jet Propulsion Laboratory
Mark Schoeberl & Peter Hildebrand & Jay HermanNASA, Goddard Space Flight Center
&Carol Raymond
NASA, Jet Propulsion Laboratory
ESDESD
Science DriversScience DriversScience Drivers
• Choice of vantage point should be driven by science needs• Some generalized science requirements that drive choice of vantage points
– High spatial resolution ( ~ 1 km or less)– High vertical resolution ( ~ 1/2 km or less)– Need for active soundings (lidar, radar)– High temporal resolution (~15 minutes)– Global coverage
• Instrument Requirements– Spectral range (Radio->UV)– Need absorption measurements
• Solar/stellar/lunar occultation• Sun glint• Artificial sources (e.g. GPS)
– Need emission measurements
• Choice of vantage point should be driven by science needs• Some generalized science requirements that drive choice of vantage points
– High spatial resolution ( ~ 1 km or less)– High vertical resolution ( ~ 1/2 km or less)– Need for active soundings (lidar, radar)– High temporal resolution (~15 minutes)– Global coverage
• Instrument Requirements– Spectral range (Radio->UV)– Need absorption measurements
• Solar/stellar/lunar occultation• Sun glint• Artificial sources (e.g. GPS)
– Need emission measurements
ESDESD
Spatial and Temporal Requirements for Earth ScienceSpatial and Temporal Requirements for Earth ScienceSpatial and Temporal Requirements for Earth Science
1 km 10 km 100 km 1000 km
1 min
1 hr
1 day
1 year
Horizontal Resolution
LEOLEO
GEOGEO
AtmosphereOcean
Land
Passive SensorsPassive Sensors
Climate & WeatherModels
Climate & WeatherModels
Mesoscale ModelsMesoscale ModelsCloud
ModelsCloud
Models
WeatherSystemsWeatherSystems
Severe StormsPollut. TransportSevere Storms
Pollut. Transport
Diurnal ChangesDiurnal Changes
TidesTides
Seasonal ChangesSeasonal Changes
StreamsStreams
PhotosynthesisPhotosynthesis
ESDESD
Some ES Measurement NeedsSome ES Measurement NeedsSome ES Measurement Needs
• Existing Measurements– Temperature / Moist– Aerosols– Vegetation canopy– Vegetation types– Crustal stress– Ocean height– Ice sheet/ Land height– Trace gases
• New Measurements– Winds– Ocean salinity– Soil moisture– Ocean mixed layer depth
• Existing Measurements– Temperature / Moist– Aerosols– Vegetation canopy– Vegetation types– Crustal stress– Ocean height– Ice sheet/ Land height– Trace gases
• New Measurements– Winds– Ocean salinity– Soil moisture– Ocean mixed layer depth
x
x
xTIR
?xx
xxxxx
xxxxxxxxx
xxxx
xxxx
xxx
Non photonic
radioradarlidarµNIRUV/Vis
TechniqueTechnique
Any vantage point Mostly LEO
ESDESD
Orbit Types Discussed HereOrbit Types Discussed HereOrbit Types Discussed Here
• Low Earth Orbit (400-900 km)• Geostationary (Geosynchronous) (~36,000 km)• L1 (Full sunlit disk) (~1,500,000 km)• L2 (Earth limb solar occultation) (~1,500,000 km)
• Low Earth Orbit (400-900 km)• Geostationary (Geosynchronous) (~36,000 km)• L1 (Full sunlit disk) (~1,500,000 km)• L2 (Earth limb solar occultation) (~1,500,000 km)
L4, L5 The Trojan points (stable)
L1, L2 Unstable Lagrange Points
ESDESD
Low Earth Orbit (LEO)Low Earth Orbit (LEO)Low Earth Orbit (LEO)• Advantages
– Polar sun synchronous• Provides global coverage once a day (reflected light) or twice a day
(active sounders or thermal IR)• Provides ~14 solar occultations a day at high latitudes
– Mid to Low -inclination• Provides more observations per day (between 2-14)• Provides ~ 14 occultations per day at varying latitudes
– Satellites can be reached by the shuttle (e.g. HST)– Active sensors (radars and lidars) can operate easily from low orbit
• Disadvantages– One to two observations per day gives poor time resolution for rapidly
changing phenomena– Global orbit-to-orbit coverage once per day requires a wide field of
view instrument– Unless special X-band receivers are available, data may have a 1-2 hour
latency.
• Advantages– Polar sun synchronous
• Provides global coverage once a day (reflected light) or twice a day (active sounders or thermal IR)
• Provides ~14 solar occultations a day at high latitudes– Mid to Low -inclination
• Provides more observations per day (between 2-14)• Provides ~ 14 occultations per day at varying latitudes
– Satellites can be reached by the shuttle (e.g. HST)– Active sensors (radars and lidars) can operate easily from low orbit
• Disadvantages– One to two observations per day gives poor time resolution for rapidly
changing phenomena– Global orbit-to-orbit coverage once per day requires a wide field of
view instrument– Unless special X-band receivers are available, data may have a 1-2 hour
latency.
ESDESD
Active SystemsActive SystemsActive Systems• Lidars
– Advantages• Altitude resolution of measurements • Specific constituents (aerosols) • Winds
– Technology challenges• Spatial coverage
– Advantages• Lots of new types of measurements (soil
moisture, ocean salinity, snow, etc.)• All weather for some types of
measurements– Technology challenges
• Large antennas needed for high spatial resolution
• Frequencies higher than 640 GHz still challenging
• Lidars– Advantages
• Altitude resolution of measurements • Specific constituents (aerosols) • Winds
– Technology challenges• Spatial coverage
– Advantages• Lots of new types of measurements (soil
moisture, ocean salinity, snow, etc.)• All weather for some types of
measurements– Technology challenges
• Large antennas needed for high spatial resolution
• Frequencies higher than 640 GHz still challenging
Results from GLAS
IceSat
400-900 km
Tropopause
ESDESD
GeostationaryGeostationaryGeostationary• Advantages
– Provides high time resolution observations– Can stare to gather photons
• 1 km Resolution at LEO => 1/7 second photon gathering time• In GEO, the same number of photons can be gathered in ~10 m• But will need larger aperture to scan the whole region in ~15 min
– Reduced cloud interference• Disadvantages
– Coverage of only about 1/5 or the earth from a single satellite• Drifting GEO (1 week orbit) solves some of this
– No polar coverage– Issues with pointing and geo-referencing
• Advantages– Provides high time resolution observations– Can stare to gather photons
• 1 km Resolution at LEO => 1/7 second photon gathering time• In GEO, the same number of photons can be gathered in ~10 m• But will need larger aperture to scan the whole region in ~15 min
– Reduced cloud interference• Disadvantages
– Coverage of only about 1/5 or the earth from a single satellite• Drifting GEO (1 week orbit) solves some of this
– No polar coverage– Issues with pointing and geo-referencing
Coverage range for quantitative data
Coverage range for quantitative data
Image coverage rangeImage coverage range
(35,875 km)(35,875 km)
ESDESD
Why GEO?Why GEO?Why GEO?
SeaWIFS July 7 SeaWIFS July 8
Smoke
SeaWIFS July 6
SmokeSmoke
GOES
QuickTime™ and a DV/DVCPRO - NTSC decompressor are needed to see this picture.
ESDESD
Daily Variability of Air PollutionDaily Variability of Air PollutionDaily Variability of Air Pollution
Diurnal variation of different trace gases near London (23.07.99-24.07.99)
0
10
20
30
40
50
60
70
80
90
0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00time [hh:mm]
NO
2 [pp
bv],
O3 [
ppbv
], SO
2 [pp
bv x
10]
0
50
100
150
200
250
300
350
400
450
CO
[ppbv]
NO2 O3 SO2 CO
LEO
GEO Solar GEO Solar
GEO TIR
CO
NO2
O3SO2
ESDESD
Diurnal Variation in Atmosphere-Surface Mass/Energy Exchange - a Key Process in Carbon and Water Cycling
Diurnal Variation in AtmosphereDiurnal Variation in Atmosphere--Surface Mass/Energy Surface Mass/Energy Exchange Exchange -- a Key Process in a Key Process in Carbon and Water CyclingCarbon and Water Cycling
Car
bon
Upt
ake
CEv
apot
rans
pira
tion
E StomatalRegulation
Links ET and C
Stomata openin response to light.
Stomata close in response to moisture stress, excess leaf temperature, and low humidity.
ESDESD
Some Example System Requirements for a Future GEO System
Some Example System Requirements for a Some Example System Requirements for a Future GEO SystemFuture GEO System
Data Flow
Assume 100 channels (bands - MODIS has 36)
Observations made every 15 minutes
Pixel Resolution 200m, 16 bits/pixel
One satellite sees 1/5 or the earth
Total data rate needed = 2 x 1010 bits/s per satellite
20 gigabits/second - can’t be done with X Band (0.15 gbs)
Optical relays or future Ka band = 2 gigabits/s
Need to move to optical or Ka band downlinks or more onboard compression and processing. These will be major drivers of future systems.
Data Flow
Assume 100 channels (bands - MODIS has 36)
Observations made every 15 minutes
Pixel Resolution 200m, 16 bits/pixel
One satellite sees 1/5 or the earth
Total data rate needed = 2 x 1010 bits/s per satellite
20 gigabits/second - can’t be done with X Band (0.15 gbs)
Optical relays or future Ka band = 2 gigabits/s
Need to move to optical or Ka band downlinks or more onboard compression and processing. These will be major drivers of future systems.
ESDESD
Lagrange Point - L1Lagrange Point Lagrange Point -- L1L1• L1 provides an ideal platform for reflected sunlight
observations• Advantages
– Near global coverage once a day– Improved signal to noise through staring– Reduced cloud interference– Narrow Field of View (0.5o) simplifies optical design – Moon calibration, enabling delicate global change
measurements spanning many years– No shadows
• Disadvantages– Limited spatial resolution vs exposure because of 0.5
km/sec Earth rotation at equator– Limited polar observations
• Technology challenges– Geo-referencing– Data rates
• L1 provides an ideal platform for reflected sunlight observations
• Advantages– Near global coverage once a day– Improved signal to noise through staring– Reduced cloud interference– Narrow Field of View (0.5o) simplifies optical design – Moon calibration, enabling delicate global change
measurements spanning many years– No shadows
• Disadvantages– Limited spatial resolution vs exposure because of 0.5
km/sec Earth rotation at equator– Limited polar observations
• Technology challenges– Geo-referencing– Data rates
Triana/DSCOVRL1 Mission
ESDESD
Lagrange Point - L2Lagrange Point Lagrange Point -- L2L2• L2 permits solar occultation of the Earth’s atmosphere from visible to 4 µ• Advantages
– Near global coverage once a day (0.1o latitude x 2o longitude)– High resolution for altitude profiles (1 to 2 km)– Good sensitivity for greenhouse gases– Can observe from middle troposphere to middle stratosphere (50 km)
• Disadvantages– Requires large (up to 8 meter) interferometer– Lowest altitude is 8 km
• Technology challenges– High speed closed loop control for Active Optics– Data rates– Thermal control of instrument
• L2 permits solar occultation of the Earth’s atmosphere from visible to 4 µ• Advantages
– Near global coverage once a day (0.1o latitude x 2o longitude)– High resolution for altitude profiles (1 to 2 km)– Good sensitivity for greenhouse gases– Can observe from middle troposphere to middle stratosphere (50 km)
• Disadvantages– Requires large (up to 8 meter) interferometer– Lowest altitude is 8 km
• Technology challenges– High speed closed loop control for Active Optics– Data rates– Thermal control of instrument
NightsideEarth
ESDESD
Future Observing SystemsFuture Observing SystemsFuture Observing Systems• LEO visible and IR sensor capability will be migrating to GEO, L1 and L2• Advantages
– Improved time resolution– Equivalent spatial resolution– Improved signal to noise through staring– Reduced cloud interference
• Disadvantages– Multi-platform needed for global coverage – Fewer polar observations– Too far out for active systems
• Technology challenges– Geo-referencing– Data rates– Large apertures needed for passive µ-wave
• Active Sensors will stay at LEO in the near future– For Geo need 3600x more power for lidars and radars assuming current
resolution and S/N
• LEO visible and IR sensor capability will be migrating to GEO, L1 and L2• Advantages
– Improved time resolution– Equivalent spatial resolution– Improved signal to noise through staring– Reduced cloud interference
• Disadvantages– Multi-platform needed for global coverage – Fewer polar observations– Too far out for active systems
• Technology challenges– Geo-referencing– Data rates– Large apertures needed for passive µ-wave
• Active Sensors will stay at LEO in the near future– For Geo need 3600x more power for lidars and radars assuming current
resolution and S/N