Imaging Instrumentation and...
Transcript of Imaging Instrumentation and...
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Imaging Instrumentation and Measurement
n Typesofinstrumentsn Typesofdetectorsn Basicinstrumentparameters
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Types of instruments
• Framing cameras
• Scanning systems – Whiskbroom imagers
• Pushbroom imagers
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Multi- and Hyperspectral Image Cubes are 3-Dimensional Data Structures
But a single detector cannot acquire all three dimensions at once.
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Framing Camera
• Simultaneous sampling
• Good geometric control
• Not suited to high spectral resolution
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Scanning Systems • Simple detector
• Easy to get multiple wavelengths
• Low detector dwell time
e.g.,Landsat1-7
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• Long detector dwell time
• Good cross-track fidelity
• No moving parts
Pushbroom Imager
e.g.,EO-1
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Semiconductor-based detectors
• Incidentradia=onexciteselectronsintoconduc=onband• Photovoltaicdevicesmeasuretheresul=ngcurrent• Photoconduc0vedevicesmeasureresul=ngchangeinconduc=vity(resistance)
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Detector Materials
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• Aisdetectorareaincm2
• ΔfisthesignalbandwidthinHz=1/(2πτ),whereτistherequiredintegra=on=me(“=meconstant”)
• NEP(noise-equivalentpower)ispowerinwaNsrequiredonthedetectortoproduceS/N=1
D*(“detec=vity”)isa“figureofmerit”forphotodetectors
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Siliconatvisiblewavelengths
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Most Common Detector Materials
• 0.4 – 1.0 µm: Silicon (Si) – E.g., Mars Reconnaissance Orbiter CRISM VNIR
• 1.0 – 5.0 µm: Indium Antimonide (InSb)
– E.g., Mars Express OMEGA
• 8 – 14 µm (or shorter IR wavelengths w/ larger x): Mercury Cadmium Telluride (Hg1–xCdxTe) – E.g., Mars Reconnaissance Orbiter CRISM IR
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Basic Instrument Parameters
Spatial, Spectral, and Radiometric Properties
• Spatial: – Instantaneous Field of View (IFOV) – Ground Sampling Distance (GSD) – Field of View (FOV) or Field of Regard – Image size (pixels)
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Importantspa+alproper+esinimages°Fieldofview(“FOV”)
-Distanceacrosstheimage(angularorlinear)°Pixelsize
-InstantaneousFieldofview(“IFOV”)SizeinmetersorisrelatedtoangularIFOVandheightabovegroundex:2.5milliradian,at1000mabovetheterrain 1000m*(2.5*10-3rad)=2.5m
Eachpixelrepresentsa~squareareainthescenethatisameasureofthesensor'sabilitytoresolveobjects
Examples: Landsat7/ASTERVIS 15meters Landsat5/ASTERNIR 30meters ASTERTIR 90meters
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Spatial Resolution
15 m/pixel 100 m/pixel 3000 m/pixel
Note: Angular resolution is an instrumental property. Spatial resolution (GSD) is an experimental property (it is determined both by the instrument and how it is used).
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Diffraction Limit
• Best possible angular resolution as a function of wavelength:
(θ is in radians)