Stennis Space Center Parameters Describing Earth Observing Remote

Stennis Space Center Parameters Describing Earth Observing Remote Sensing Systems Robert Ryan Lockheed Martin Space Operations - Stennis Programs John C. Stennis Space Center December 2 -4, 2003 1

Contributors Stennis Space Center NASA Stennis Space Center Vicki Zanoni Mary Pagnutti NASA Goddard Space Flight Center Brian Markham Jim Storey 2

Introduction Stennis Space Center • Standard definitions for spatial, spectral, radiometric, and geometric properties are needed describing passive electro-optical systems and their products. • Sensor parameters are bound by the fundamental performance of a system, while product parameters describe what is available to the end user. 3

Introduction (Continued) Stennis Space Center • Because detailed sensor performance information may not be readily available to an international science community, standardization of product parameters is of primary importance. • User community desire as a few parameters as possible to describe the performance of a product or system. 4

Introduction (Continued) Stennis Space Center • Guidelines and standards are of little use without standardized terms. • Studies that describe the impact of parameters on various applications are critically needed. • This presentation is going to emphasize spatial. 5

Specifying a Digital Imagery Product Stennis Space Center • Spatial – Spatial/Frequency Domain – Aliasing • Spectral (Sensor) – Panchromatic or Multispectral • Radiometry – Relative – Absolute – Signal-to-Noise Ratio • Geolocational Accuracy – Circular Error 6

Some Spatial Product Parameters Stennis Space Center • • • Ground Sample Distance Point Spread Function Edge Response Line Spread Function Optical Transfer Function – Modulation Transfer Function (MTF) • Aliasing 7

Ground Sample Distance Stennis Space Center • Ground Sample Distance (GSD) is the distance between the center of pixels in an image – Products are typically resampled and do not completely agree with intrinsic sensor sampling • Most commonly used spatial parameter • Does not tell the whole story 8

0. 2 m GSD 0. 4 m GSD Stennis Space Center 0. 6 m GSD 1. 0 m GSD 9

GSD 0. 2 m 2 x 2 GSD 0. 2 m 3 x 3 GSD 0. 2 m 4 x 4 Stennis Space Center 10

Point Spread Function Stennis Space Center • Scene is considered to be a collection of point sources • Each point source is blurred by the point spread function (PSF). System Point source A Impulse Response (PSF) Displaced Point Spread Function 11

Image Formation Stennis Space Center • Image is convolution of point spread function (PSF) with input scene 12

Optical Transfer Function Stennis Space Center • An equivalent measurement of the PSF is the Optical Transfer Function via a two dimensional Fourier Transform – Consists of Magnitude and Phase Terms 13

Modulation Transfer Function Stennis Space Center • MTF is a measure of an imaging system’s ability to recreate the spatial frequency content of scene MTF is the magnitude of the Fourier Transform of the Point Spread Function / Line Spread Function. 1. 0 Cut-off Spatial frequency 14

Stennis Space Center 15

Spatial/Frequency Domain Stennis Space Center • Most specifications are written in terms of MTF as a function of spatial frequency – Dominant parameter is typically MTF @ Nyquist frequency – Nyquist frequency depends on GSD • Nyquist frequency = 1/(2*GSD) – MTF at Nyquist is a measure of aliasing • Edge Response is more intuitive – RER (Relative Edge Response) – Ringing 16

Edge Response and Line Spread Function Stennis Space Center 17

Relative Edge Response Stennis Space Center 1. 2 Ringing Overshoot Edge Response 1 0. 8 0. 6 0. 4 Region where mean slope is estimated Slope is approximately inversely proportional to width of PSF 0. 2 0 Ringing -0. 2 Undershoot -2. 5 -2. 0 -1. 5 -1. 0 -0. 5 0 0. 5 Pixels 1. 0 1. 5 2. 0 2. 5 Edge slope is a simple description applicable for well behaved systems 18

Stennis Space Center Aliasing 19

Assessing Levels of Aliasing 1 L 0 1 0 GSD/L= (GSD) (Slope) << 1 No Aliasing GSD L 0 1 Stennis Space Center GSD/L= (GSD) (Slope) ~ 1 Moderately Aliased GSD PSF L GSD/L= (GSD) (Slope) > 1 Severely Aliased GSD Nyquist Sampling: Need to sample at least twice the highest spatial frequency to reconstruct image 20

CIR Images of SRS Synthesized Products Stennis Space Center Savannah River Site - 28. 8 GSD Simulations AVIRIS 3. 2 m GSD 28. 8 m PSF, Slope 0. 035 m-1 9. 6 m PSF, Slope 0. 10 m-1 16 m PSF, Slope 0. 06 m-1 35. 2 m PSF, Slope 0. 028 m-1 41. 6 m PSF, Slope 0. 024 m-1 22. 4 m PSF, Slope 0. 045 m-1 48 m PSF, Slope 0. 021 m-1 21

Landsat Spatial Resolution Trade Study Stennis Space Center NDVI 1. 0 0. 8 AVIRIS: ~3 m GSD, ~3 m PSF After ETM+ Band Synthesis After 3 x 3 Boxcar Averaging: ~10 m GSD, ~10 m PSF Actual Landsat 7 ETM+: 30 m GSD, ~36 m PSF 0. 6 0. 4 0. 2 After Additional 3 x 3 Filtering: ~10 m GSD, ~30 m PSF After Additional 3 x 3 Decimation: ~30 m GSD, ~10 m PSF After Additional 3 x 3 Averaging: ~30 m GSD, ~30 m PSF 22

Spatial Parameter Summary Stennis Space Center • Basic Description Well Behaved Systems – In track and cross track • GSD, Edge Slope • GSD, PSF FWHM • GSD, MTF @ Nyquist • Full Description – GSD and 2 D PSF or OTF 23

Spectral Stennis Space Center • Basic Description – Center Wavelength – Full width half maximum – Slope edge at 50% points • Others – Ripple – Out-of-band rejection • Full Description – Spectral response functions with units 24

Spectral Characteristics: Bands. Stennis Space Center System Spectral Response Band-to-Band Registration 25

Radiometry Specification Stennis Space Center • Three Types – Linearity – Relative • Pixel-to-Pixel • Band-to-Band • Temporal – Absolute • SNR 26

Radiometry: Linearity Stennis Space Center Linear and non-linear response to input radiance 27

Radiometry: Relative Stennis Space Center Normalized Average Row Values for Antarctica IKONOS Image of Antarctica – RGB, POID 52847 28 Includes material © Space Imaging LLC

Radiometry: Absolute Stennis Space Center NIR Band Calibration Summary 30 Radiance [W/(m 2 sr)] 25 20 15 SSC, Big Spring, TX, 6/22/01 SSC, Big Spring, TX, 8/5/01 SSC, Lunar Lake, NV, 7/13/01 SSC, Lunar Lake, NV, 7/16/01 SSC, Maricopa, AZ, 7/26/01 SSC, Stennis, 52 tarp, 1/15/02 SSC, Stennis, 3. 5 tarp, 1/15/02 SSC, Stennis, 22 tarp, 1/15/02 SSC, Stennis, Concrete, 1/15/02 SSC, Stennis, Grass, 1/15/02 SSC, Stennis, 52 tarp, 2/17/02 SSC, Stennis, 3. 5 tarp, 2/17/02 SSC, Stennis, 22 tarp, 2/17/02 SSC, Stennis, Concrete, 2/17/02 SSC, Stennis, Grass, 2/17/02 Uof. A/SDSU, Brookings, SD, 7/3/01 Uof. A/SDSU, Brookings, SD, 7/17/01 Uof. A/SDSU, Brookings, SD, 7/25/01 Uof. A, Lunar Lake, NV, 7/13/01 Uof. A, Lunar Lake, NV, 7/16/01 Uof. A, Railroad Valley, NV, 7/13/01 Uof. A, Railroad Valley, NV, 7/16/01 Uof. A, Ivanpah, CA, 11/19/01 SI Calibration Curve, Post 2/22/01 SI Radiance = DN/84. 3 10 5 0 0 200 400 600 800 1000 DN 1200 1400 1600 1800 2000 29

Signal-to-Noise Ratio Stennis Space Center • Several definitions exists • For well behaved systems (Very few bad detectors) Basic Description – Temporal Noise or Shot Noise Limited – SNR for an extended uniform radiance scenes • Advanced Description – Includes both detector nonuniformity, processing and shot noise components 30

Pan Band MTFC Pan Kernel Stennis Space Center Pan Kernel Column Section Pan Kernel Row Section 5 5 4 4 3. 5 3 3 2. 5 2 2 1. 5 1 1 -0. 5 -0. 4 -0. 3 -0. 2 -0. 1 0. 2 0. 3 0. 4 0. 5 Cycles/ Pixel Row MTFC slightly stronger 31

Noise Gain Stennis Space Center SNR decreases with MTFC processing and the noise displays a spatial frequency dependence that did not exist at the sensor Band Noise Gain Blue 1. 59 Green 1. 63 Red 1. 68 NIR 1. 81 Pan 4. 16 MTFC OFF SNR 25 MTFC ON SNR 13 NIR Kernel Applied to Simulated Imagery 32

Spatial Resolution: SNR Stennis Space Center Original Maricopa IKONOS Imagery SNR ~ 100 Maricopa IKONOS Imagery with Noise Added SNR ~ 2 33 Includes material © Space Imaging LLC

Geolocation Accuracy Stennis Space Center • Basic Description – RMSE – Circular Error (CE 90, CE 95) • Full Description – Distribution Functions 34

CE 90 Geolocational Accuracy Stennis Space Center • A standard metric often used for horizontal accuracy in map or image products is circular error at the 90% confidence level (CE 90). The National Map Accuracy Standard (NMAS) established this measure in the U. S. geospatial community. NMAS (U. S. Bureau of the Budget, 1947) set the criterion for mapping products that 90% of welldefined points tested must fall within a certain radial distance. Includes material © Space Imaging LLC 35

CE 90 Example Stennis Space Center 36

Summary Stennis Space Center • For “well behaved” systems and products a few simple well chosen parameters can describe the system or product. • Derived products can be significantly different than their intrinsic sensor data • Studies that describe the impact of parameters on various applications are critically needed. 37