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ECE 583Lecture 26
Imaging Visible and Infrared Radiometers
Multi-Spectral AnalysisActive/Passive
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Ash Plume across the North AtlanticApril 15, 2010
MODIS
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Elevated MODIS Aerosol Optical Depth near Iceland volcanic eruptionGiovanni AOD images and time-series show increase near location of eruption,
coinciding with eruption onset
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Aerosol retrieval from space- the
MODIS aerosol algorithm
Uses bi-modal, log-normal aerosol size distributions.
5 small - accumulation mode (.04-.5 m) 6 large - coarse mode (> .5 m)
Look up table (LUT) approach
15 view angles (1.5-88 degrees by 6)
15 azimuth angles (0-180 degrees by 12)
7 solar zenith angles
5 aerosol optical depths (0, 0.2, 0.5, 1, 2)
7 modis spectral bands (in SW)
Ocean retrievals
compute IS and IL from LUT
find ratio of small to large modes ()andthe aerosol model by minimizing
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then compute optical depth fromaerosol model and mode ratio.
and Im is the
measured radiance.
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Example: reflection of sunlight from a
plane parallel atmosphere
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Cloud
or aerosol
Surface
Multiple layers aerosolsurface contrast
The Problem:
Optical depth is obtained through the
relationship between reflected sunlight andoptical depth
To do so requires that reflections from
surface be removed.
This is difficult when there is littlecontrast between the surface and cloud oraerosol
Low contrast conditions occur frequently-e.g thin layers of cloud or aerosol overland, cloud over snow/ice
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Land retrievals
Select dark pixels in near IR,
assume it applies to red and blue
bands.
Using the continental aerosol model,derive optical depth from the red
and blue bands (LUT approach
including multiple scattering.
Determine aerosol model usingsingle-scattering relationship
Adjust the optical depth according
to the new aerosol model.
The key to both ocean and
land retrievals is that the
surface reflection is small.
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Measurement Requirements for Imaging Radiometers
Spatial resolution (pixel size)
Number and wavelength of channels
Spectral width of wavelength channels
Spatial alignment (registration) between wavelength channels
Minimum signal measurement accuracy (%)
Measurement accuracy of radiance (calibration)
Basic Type of Image Scanning Radiometer
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Types of Optical Scanning
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Whiskbroom Imaging
Pushbroom Imaging
Grating Spectrometer Pushbroom Imaging
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Instrument Requirements for Imaging Radiometers(Derived from measurement requirements)
Instantaneous Field-of-View IFOV = d/R d Pixel resolution dimension
requirement
R Satellite nadir altitude
Line Frequency (mirror RPM) fL= V/d V Satellite velocity
Angular Rate v = 2/ fL (radians / second)
Sample Rate fc = v/ IFOV
Detector Electronic Bandwidth fb = fc/ 2 Nyquist frequency
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Accuracy Requirement: Signal/Noise = 1 at minimum signal error or resolution (watts orTbrightness temperature ). Noise is the combination of signal shot noise and detector noise (as seenbefore).
Signal S at detector in watts:
S () = Ipix() A [(IFOV)2/4] Ts Ipix() Spectral Intensity of pixelTs System optical transmissionA System effective aperture area
- Spectral Band pass requirementCalculated Aperture Requirement : Area calculated from Smin signal noise and Ipix,min measurementrequirement
Ar = Smin/(Imin A [(IFOV)2/4] Ts )
Higher spatial or spectral resolution requires larger aperturesHigher spatial resolution also requires faster scan rate and signal bandwidth, increasing noise.
But, multi element detectors increase through put by N the number of detectors, reducing theaperture requirement correspondingly.
Instrument Requirements for Imaging Radiometers(Derived from measurement requirements)
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ER-2 Cloud and Aerosol Observation Experiment
Science Applications (1983-2000)
Height Structure from Lidar
Multi Sensor Observation Experiment
VIS
IR
Multi Spectral Radiance
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Spatial Resolution:20 m
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10.7 m2.16 m
1.64 m
0.76045 m
0.76346 m
0.75392 m
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Stephens, Remote Sensing of the Lower Atmosphere, Chapter 6
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Lidar and IR Radiance TechniqueActive/Passive Sensing
Multispectral Analysis of Cloud Particles
Thermal IR Cirrus Parameter Sensing
Temperature
BackscatterSource Function of IR Radiance
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Thermal IR Particle Size
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SPINHIRNE ET AL.: CONTRAIL CIRRUS FROM AIRBORNE REMOTESENSING, GRL 1998
Contrail Sensing Example
MODIS Airborne Simulator Data
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Data MiningForty-three years after the Nimbus IIsatellite collected these data, a team fromNSIDC and NASA recovered a globalimage from September 23, 1966. In thisview over Antarctica, overlaid on GoogleEarth, the Ross Ice Shelf appears clearly
at left.
Early Weather Imaging Radiometers
HRIR High Resolution Imaging Radiometer
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The single-channel dual-band pass scanning radiometer
uses a PBSe photoconductive detector cell and providesmeasurements of blackbody temperatures 210K 330K. TheScan mirror is inclined to 45 degrees with a scan rate of 44.7revolutions per minute. The Instantaneous field of view is 8.8milliradians and the scan line separation is 8.3 km. Theground resolution is 8 km at 1110 km.
The Nimbus III HRIR was designed to allow nighttime anddaytime cloud cover mapping by use of dual band-pass filterwhich transmits 0.7 to 1.3 micron, and 3.4 to 4.2 micronemitted radiation. The improvement of detector temperaturecontrol and electronics compensation has eliminated themultiple calibrations of previous instruments.
Early NASA Experimental Meteorological SatelliteNimbus I VII Launched (1964 1978)
Data Operations through 1994Some instruments:
Nimbus II Medium Resolution Infrared Radiometer (MRIR) (4.6-6.9 micron, 10-11 micron, 14-16 micron, 5-30 micron, 0.2-4.0 micron)
Nimbus II High Resolution Infrared Radiometer (HRIR) (3.5 to 4.1 micron)
Nimbus III single-channel dual band-pass High Resolution Infrared Radiometer (HRIR) (3.4 4.2 micron at nighttime, 0.7-1.3 micron at daytime)
Nimbus III Medium Resolution Infrared Radiometer (MRIR) (4.5-7.0 micron, 10-11 micron, 14.5-15.5 micron, 20-23 micron, 0.2-4.0 micron)
Nimbus IV Temperature and Humidity Infrared Radiometer (THIR) at 11.5 micron channel
Nimbus IV Temperature and Humidity Infrared Radiometer (THIR) at 6.7 micron channel
HRIR
Nimbus 3 Image of Australia (1969)
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NOAA 14 19 1994 to 2009
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NOAA-19 CharacteristicsMain body: 4.2m (13.75 ft) long, 1.88m (6.2 ft) diameter
Solar array: 2.73m (8.96 ft) by 6.14m (20.16 ft)Weight at liftoff: 1419.8 kg (3130 pounds) including 4.1 kg of gaseous nitrogen
Launch vehicle: Delta-II 7320-10 Space Launch Vehicle
Launch date: February 06, 2009 Vandenburg Air Force Base, CAOrbital information: Type: sun synchronous
Altitude: 870 kmPeriod: 102.14 minutesInclination: 98.730 degrees
Sensors:Advanced Very High Resolution Radiometer(AVHRR/3)Advanced Microwave Sounding Unit-A (AMSU-A)
Microwave Humidity Sounder (MHS)High Resolution Infrared Radiation Sounder (HIRS/4)
Solar Backscatter Ultraviolet Spectral radiometer (SBUV/2)Space Environment Monitor (SEM/2)Search and Rescue (SAR) Repeater and ProcessorAdvance Data Collection System (ADCS)
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AVHRR Advanced Very High Resolution Radiometer
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Imaging Radiometer Detectors
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Remote Sensing Group University of ArizonaThe Remote Sensing Group in the College of Optical Sciences at theUniversity of Arizona is best known for its work on the in-flight,
radiometric calibration of remote sensing imagers using ground-basedmeasurements at desert test sites. Radiometric calibration in thiscontext refers to the ability to take the data from a sensor and convertit to a standard energy scale. Such work allows for the comparison ofdata from an array of imagers (by last count more than 30 sensors).The methods of the group have been in use since the mid-1980s and
currently provide absolute radiometric calibration to better than 2%,both in accuracy and precision in the mid-visible.
Visible and near IR
Radiance Calibration
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Terra Satellite
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MODIS
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VIRS on NPOESS follows MODIS
Vincent V. Salomonson et al.
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Earth Observing System (EOS) PM Formation
Aqua EOS main platform with six imagers and sounders, UV microwaveAura EOS main stratospheric platform with 4 sounding instrumentsParasol CNES polarization imager
Cloudsat Cloud RadarCalipso Cloud LidarOCO Orbiting Carbon Observatory
GLORY- NASA Aerosol Polarization Imager
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1 nm
A-band
Wavelength index
Ref
lection
The key is to make measurements
at high spectral resolution(0.01- 0.1 nm).
Actual aircraft data
from OBrien et al (1998)
Example OCO: Aerosol retrieval from oxygen absorption
Optical Depth of Overlapping
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Optical Depth of OverlappingLayers
This is actual satellite data from MOS.
With better resolution (such as PABSI),
profiling of layers becomes even
more capable
Coded in A-band spectra is information
about cloud and aerosol layering
Optical Depth Under
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Optical Depth UnderLow Contrast Conditions
Simulation of PABSImeasurement
for thin aerosol layer
overlying
land surface
Red wavelengths respond mostly to surface albedo changes(reflecting the capabilities of most existing instruments)
Yellow wavelengths respond mostly to aerosol changes.
Key point: The ability to see into the absorption lines provides a way of
discriminating surface from atmosphere.
Thus surface reflection as well as optical depth is obtained
from PABSI.
wavenumber cm-1sensitivity to
optical depth
sensitivit
y
to
surfacea
lbedo
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aerosol optical depth error surface albedo error
absolute
err
or
relative
erro
r
Aerosol retrieval is difficult:
small signature in observed
spectrum. instrument noise.
instrument convolution
(smearing or averaging of
observations).
uncertainties in a priori data.
Retrieval simulation
Best case scenario
(assume we know asymmetry
parameter, single-scattering
albedo, and location of aerosol
layer).