envi training - goozmo, boulder colorado company · 1 envi training itt visual information...

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ENVI Training

ITT Visual Information Solutions

Topographic Production Capability

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ENVI

• ENVI 4.8 with ENVI Zoom– 3‐window “classic” interface.

– One‐window "Zoom" interface with pan and zoom functionality.

– Can launc Zoom or classic from the other interface in a linked session.

– 4.8 introduces Viewshed Workflow, LiDAR viewer, and ENVI tools for ArcGIS®


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Notes on Organization

• We’ll be taking one long break for lunch and a couple of short breaks throughout the day.

• Training will be organized to go through guided workflows, followed up by challenge exercises.

• A comprehensive set of ENVI capabilities will be organized into scenario‐based training.

• A few standalone module sections at the end will cover Orthorectification, DEM Extraction, SPEAR, and THOR tools.


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Disaster Mitigation ScenarioUsing change detection to guide

reconstruction efforts post‐Tsunami.


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Indian Ocean Tsunami Analysis

In the immediate aftermath of the 2004 Indian Ocean Tsunami, image analysis played a key role in assessing damage caused by windstorm, flood and storm surge.


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The extracted coastal damage assessment information was then available to GIS users and rescue personnel in their applications to quantify and classify the extent of the damage.

Indian Ocean Tsunami Analysis


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Analysis Workflow

• Display and Subset Imagery

• Orthorectification

• Image to Image Registration

• Visualize and explore the imagery

• Perform Change Detection


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Subsetting Imagery

• Using Resize Data tool in ENVI

• Spatial and/or Spectral subset

• Spatial subset:– by image

– by coordinates

• Other options– by size of another file

– by Region of interest or

vector file


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Image Rectification

• Many tools in ENVI


• Image to Map Registration

• Convert and customize map projections

• Coordinate Converter

• Orthorectification– RPC

– Rigorous (separate module)


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Image Rectification Exercises

• RPC Othorectification– Account for distortions are caused by topography, camera geometry, etc.

– Typically requires:• Image with approximate geolocation information

• RPC model in ancillary file

• Elevation information (DEM)

• Offset between mean sea level and the gravitational potential surface (known as the geoid), so the


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Image Registration Exercises

• Image to Image Registration– Selection of Ground Control Points

– Warping and Resampling

Time 1 ImageTime 2 Image


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• Image Difference or Thematic Change

• Use vegetation indices if desired

• Cleanup methods for filtering and aggregating results

• Preview changed areas in portal window

Change Detection Workflow


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Change Detection• Two change detection algorithms in

ENVI Zoom– Thematic Change – takes two classification images and identifies differences between them. The resulting classification image shows class transitions, for example, from vegetation class to urban class.

– Image Difference ‐ compares two images taken at different times, and it identifies differences between them. The difference can be computed on a specified input band or on a feature index (e.g., veg), with optional thresholding


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Change Detection

• Thresholding– Automatic methods

– Manual sliders

• Cleanup step – Smoothing

– Aggregation


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Change Detection

• Export– Classification image

– Vectors (shapefiles) HLZ.pptx


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Ship Landing ScenarioUsing ENVI to select suitable regionsfor shore approach.


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Ship Landing Scenario

• Commercial data import– Combine individual bands into one file and reorder

• Image Mosaicking • SPEAR Relative Water Depth

– Masking• Density Slice• Export to ArcGIS


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Relative Water Depth Product

SPEAR ‐ Relative Water Depth

• Generate a product depicting relative water depths (shallow to deep) for a region of interest

• Log ratio or principal components analysis methodologies

• Bottom albedo independent algorithm means sea floor brightness does not affect depth estimates

• Optional absolute depth calibration using ground truth

Quickbird MSI


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Ship Landing Scenario• Data import

– Combine individual bands into one file and reorder

• Image mosaicking


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Ship Landing Scenario ‐ results

• SPEAR Relative Water Depth

– Color tables

– Density slice

• Density Slice


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Helicopter Landing Zone Scenario

• Using ENVI’s LiDAR and Topographic Modeling Capabilities to Determine Areas Where a Blackhawk Helicopter can be landed.


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HLZ Requirements

• Exclude areas near Vertical Obstructions

• Exclude Water cover.

• Exclude areas of excessive slope or with otherwise unsuitable topography.

• Combine all exclusions into a single rule image.

• Select areas of appropriate morphology for the helicopter in question (area, shape, etc.)


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ENVI Capabilities

• Use the LiDAR Viewer to gain actionable intelligence.

• Construct a vertical obstructions layer using Band Math.

• Mask out water by digitizing vectors aided with region growing.

• Create buffer zones around water and vertical obstructions.


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ENVI Capabilities

• Perform topographic modeling.

• Threshold out unsuitable data ranges to an ROI.

• Use convolutions and morphology to locate appropriately sized areas for the landing zone.


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What is LiDAR?• Light Detection And Ranging

• You may also see the terms Laser Altimetry or ALSM (Airborne Laser Swath Mapping)

• LiDAR sensors function by reflecting a dense array of laser beams over a surface and using them to record information about that surface.


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LiDAR Datasets

• Image analysts work with LiDAR data after it has been preprocessed and turned into elevation raster images.

• DEM, DTM, DSM, and Intensity Image are all names you will see for datasets derived from LiDAR point clouds.


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DSM

• The DSM (Digital Surface Model) is the most widely available LiDAR raster product. It is produced through a simple interpolation process, and contains elevation data for objects such as buildings and trees in addition to terrain.


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DTM

• A DTM (Digital Terrain Model) is produced through LiDAR processing which filters out buildings, trees, and other above‐ground objects from a DSM to produce a layer which contains only ground elevation values.


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LiDAR Viewer in ENVI

• ENVI 4.8 introduces a new high-performance LiDAR viewer• Efficiently use imagery for intelligence and actionable information


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• Measure building height and volume

• Determine elevation• Visual Interpretation


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Deriving New LiDAR Data• When working with

LiDAR data, you may need to use basic image processing tools to create other layers.

• One simple example is that of the Feature Height layer, which is created by subtracting the DTM from the DSM.


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Threshold to ROI

• Specific data ranges can be used to construct ROIs when using the Threshold to ROI tool.

• For the HLZ, we can use it to identify areas which contain vertical obstructions by thresholding out feature height above a certain value.


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ROIs and Region Growing

• If simple values cannot be used to mask out areas, then ROIs can be digitized.

• For objects like water bodies which are spectrally homogeneous, region growing can be used once an area inside the feature is digitized.


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Topographic Modeling

• Slope, Aspect, and other topographic measures can be extraction from a DEM in ENVI.

• Use Threshold to ROI with these tools to mask out desirable or undesirable values.


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Band Math in ENVI

• Band Math is a multi purpose tool which can be used to combine datasets, extract information from various datasets, or compare datasets.

• Don’t overestimate the difficulty of using the band math tool. Most operations use only basic arithmetic.


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ENVI Morphology Filters

• Can use Erode to shrink or reduce islands of smaller pixels, or Dilate to fill, expand, or fill holes in an image.

• Morphology filters provide the capability to automatically filter out areas of potential helicopter landing zones that are too small to accept helicopters of a certain size.


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Forest Clearance Scenario

• Using ENVI to locate regions where forest has been cleared.


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Forest Clearance Scenario

• Can be used to locate and assess:

• Agricultural expansion.

• Illegal logging or production of illegal drugs.

• Construction or expansion of facilities.


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Forest Clearance ‐ Logistics

• Forest clearance can be detected from a variety of sensors – presence of NIR and Red bands are critical.

• Forgiving of limits to spatial resolution of the sensor.

• Easily performed on common free, government, and commercial data formats.


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Forest Clearance – ENVI components

– Data conversion to radiance or reflectance– Atmospheric correction – Masking cloud cover, water, etc.– Register images– Image Difference Workflow : the difference can be computed on a vegetation index (NDVI).

– Threshold, Cleanup, and Export Results.


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Sensor Calibration and Atmospheric Correction


10-6 nm

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The Electromagnetic Spectrum and Atmospheric Transmittance in the Visible, Near Infrared and Short Wave Infrared

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Masking, ROIs, Region Growing

• If simple values cannot be used to mask out areas, then ROIs can be defined.

• For objects like clouds which are spectrally homogeneous, region growing can be used once an area is drawn in.


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NDVI

• Use vegetation’s spectral properties to assess health and vegetation types.

• Relies on peak in NIR and valley in Red.


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Image Rectification

• Many tools in ENVI


• Image to Map Registration

• Convert and customize map projections

• Coordinate Converter

• Orthorectification– RPC

– Rigorous (separate module)


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Image Rectification –Nearest Neighbor Resampling

• Original scene and the newly rectified scene

2. Output image with GCPs

3. Source image laid over output image with GCPs aligned

4. Pixel values from the input are assigned to pixels in output byresampling

1. Source image with GCPs

GCP

GCP


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Image Rectification – ResamplingImage Rectification – ResamplingGrid Nearest Neighbor

Bilinear Cubic Convolution

Original imageWarped image


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Forest Clearance: Change Detection

• Guided workflow in ENVI Zoom.

• Compute Feature Index Difference.

• Threshold Difference Image.

• Cleanup classification image.

• Export to vectors.


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ENVI Tools: further integration with ArcGIS®

• Image analysis tools can now be accessed directly from ArcGIS

• ENVI tools work in both Server and desktop environments

• Support for ArcGIS 9.3 and 10

ENVI Tools

Can be accessed from the ArcGIS Desktop

Also from the ArcGIS Server®

Platform


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D

Tools include:• Detecting Change• Extracting Features• Classifying land cover

• Create custom ENVI Tools

• Upon installation of ENVI, image processing tools will appear in ArcGIS

ENVI 4.8: Streamlined workflow and further integration with ArcGIS®


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– Rosse Ice Shelf, Antarctica– Change detection from 2005-2008

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• Blue areas = new, positive, change• Red areas = removed, negative

change

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Orthorectification

• A process that accurately registers image pixels to ground coordinates and removes geometric distortions induced during image capture– Causes of geometric distortions

• Variable scene topography• Off-nadir sensor acquisition geometry• Platform instability or inaccurate knowledge of pointing

geometry

• Result: An image product with properties of a map– Projected to map coordinate system (e.g., UTM)– Constant scale


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Applications of Orthoimagery

• Orthoimagery is essential for:– Accurate point coordinate determination– Object measurement (size, shape)– Precise collection of feature data for mapping applications

• Orthoimagery is often used as an image base in Geographic Information Systems (GIS)– Positional accuracy required for registration with map layers– Imagery often provides the most up-to-date information to map

users


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ENVI Orthorectification Methods

• RPC-based Method (Rational Polynomial Coefficients)– Uses an approximate sensor model to construct the

geometry relating an image pixel (sample, line) to a map coordinate (X, Y, Z)

• Rigorous Sensor Model Method– Uses the exact sensor model defined by detailed

interior and exterior orientation parameters– Combines several analytical sub-models that:

• Construct a look vector for each image pixel • Intersect the vector with the earth ellipsoid• Project the intersection to a map coordinate system

– Multiple imagesTopographic Production Capability

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ENVI RPC OrthorectificationRequired Inputs:

– Image– RPC data– Elevation– Geoid offset for

correct elevationOptional Inputs:

– Digital Elevation Model (DEM)

– Ground Control Points (GCPs)


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Features and functionality:• Rigorous Sensor Models

• Wizard‐Based GUI Workflow

• Block Bundle Adjustment

• GCPs for Model Adjustment

• Reorder Images & Define Cutlines

• Automatic Tie‐Point Generation (requires RPCs)

Supported sensors:• ASTER Level 1B• LANDSAT 5 (TM) and 7 (ETM+)• IKONOS & OrbView-3• GeoEye-1• QuickBird• SPOT DIMAP• WorldView-1• RADARSAT-1• EROS-A, ERS, CARTOSAT-1,

FORMOSAT-2, KOMPSAT-2• Vexcel UltraCam & Applanix DSS• RPC Support• Generic Frame Camera• Customizable

ENVI – Rigorous Orthorectification Module


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Simple Workflow

• Five step wizard-based workflow– Select Input Imagery and DEM– Collect and Edit GCPs– Select Image-to-Image Tie Points– Order Images and Define Cutlines– Set Output Parameters


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Project Management

• Save and Restore Project Files

• Layout Manager– View spatial relationship of

imagery, DEM, GCPs and tie points

– List input data sets• Error Visualization

– View residual errors in tabular and map form


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ENVI - DEM Extraction Module

The ENVI DEM Extraction Module allows you to easily create accurate digital elevation models from stereo imagery• Wizard-based tool walks you

through all the necessary steps

• Flexibility allows you to edit, extract features, and more


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DEM Extraction: Anaglyph Imagery

• Stereo pairs can be used to create a stereoscopic 3D image which can be viewed with anaglyph glasses.

• Each eye sees a slightly different picture based on chromatically opposite colors and the brain blends the image together.


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How DEM Extraction Works

• Creation of Epipolar Images. Epipolar geometry describes the geometrical constraint between two frame images of a stereo pair.

• Image matching: locate points on both left and right images which correspond to the same ground feature.

• DEM Geocoding – The DEM must be oriented in a geographic or projected coordinate system.

• Relative or absolute DEM – whether or not DEM is calibrated to ground truth elevation.


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LAS LiDAR to DEM

• LiDAR point clouds contain a lot of information, but 2D gridded formats allow a lot of quick topographic processing.

• ENVI supports import of LiDAR LAS files into a gridded format.


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DEM Creation

• From point cloud, to TIN, to Raster.

• First vs. Last return biases.


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• LiDAR results contain above surface features.

• End product can be used for topographic modeling, Orthorectification, etc.


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Image to Map Registration



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Image to Map Registration

• Picking Ground Control Points– Fractional pixel possible with zoom window

• Warping

• Resampling

• RMS error – based on GCPs so not a direct measure of accuracy


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Image to Map Registration• Ground Control Points

Image

Map


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Warping Methods• Rotation, Scaling, Translation

– Affine transformation (straight and parallel lines maintained)– O‐order polynomial– Need at least 3 GCPs

• Polynomial Function– Allows shearing– Up to order n where GCPs>(n+1)2

– Need at least 4 GCPs– Shouldn’t go higher than 4th order – “over fit”

• Delaunay Triangulation– Warp model varies with triangle– Output limited to outermost GCPs ‐ However, can use Predict

feature


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Image Resampling AlgorithmsImage Resampling AlgorithmsGrid Nearest Neighbor

Bilinear Cubic Convolution


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Resampling

• Nearest Neighbor– Preserves radiometry

– Pixilated output

• Bilinear Interpolation– Smoother lines

• Cubic Convolution– Smoother lines

– More computationally intensive


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SPEAR Tools



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SPEAR Workflows• Change Detection (3 types) • Lines of Communication (water and roads)• Pan Sharpening• Relative Water Depth• Spectral Analogues• Terrain Categorization (TERCAT)• Vegetation Delineation• Watercraft Finder• Anomaly Detection • Google Earth Bridge• Terrain‐based Orthorectification• Image‐to‐Map Registration• Metadata Browser • Independent Component Analysis• Image Segment Mosaicking• Vertical Stripe Removal


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SPEAR Provides Guided Image Exploitation

• Stand‐alone GUI modules

• Textbox with descriptive instructions

• File I/O including spatial subsetting

• Prompt buttons and alerts to assist processing


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Processing Workflow

User is guided through processing one step at a time


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SPEAR ‐ Pan Sharpening• Streamlines creation of high‐resolution color images from

Pan and MSI inputs

• Semi‐automated image coregistration

• Gram‐Schmidt sharpening algorithm accurately preserves MSI color information

+ + =

High Spatial res.Low Spectral res

Low Spatial res.High Spectral res

High Spatial res.High Spectral res

SPEAR Processing


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SPEAR ‐ Pan Sharpening

• Image Registration step– Evaluation of GCPs


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SPEAR Workflows ‐ TERCATTERCAT – Terrain Categorization

– Create Regions of Interest to match to

– or perform unsupervised classification


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TERCAT cont’d• Many SPEAR routines offer atmospheric correction

– Dark Object Subtraction is appropriate for multispectral data

Range of Atmospheric Scattering

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TERCAT Results

Maximum likelihood Maximum likelihoodfiltered


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SPEAR Spectral Analogue

• Collect spectra from ROIs in scene

• Algorithms ‐Spectral Angle Mapper, Matched Filter, and MF/SAM Ratio


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LOC – Roads

• Spectral processing highlights roads to aid digitizing – using the Intelligent Digitizer

• Supervised mapping:– Atmospheric correction– User selects training pixels for

mapping water– roads mapped using SAM, MF and

MF/SAM ratio

• Unsupervised mapping:– Principal Components Analysis– Red soil

• Digitized vectors exported to Shapefile for use in GIS– export to ArcGIS

SPEAR derived LOC


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THOR Workflows



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THOR Tools

• Enable novice analysts to effectively exploit hyperspectral data

• “SPEAR‐like” workflows for hyperspectral data processing


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THOR

• Will work with any reflectance hyperspectral data that ENVI will read– Automatically extracts metadata from ARTEMIS NITF data

– Fully supports all data written in NGA’s HSI NITF standard

• Place existing tools within ENVI into user‐friendly workflows

• Add new twists to old tools


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THOR Modules

General Utility Modules:• Anomaly Detection• Atmospheric Correction• Change Detection• LOC – Water and Trails• Stressed Vegetation• Target Detection• Material Identification• THOR Spectral Library Builder• THOR Spectral Library Viewer• Transform Band Weights


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THOR Workflows• Each module is a

workflow consisting of a number of steps (some steps are optional)

• Each step prompts user to perform specific actions

• At the end of the workflow, the product is complete


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Target Detection Module

File SelectionAtmos. CorrectionTarget SelectionBackground +/‐Dimensionality ReductionSignature MatchingRule ThresholdingSpatial FilteringExport TargetsProcessing

Complete


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Atmospheric Correction• Auto‐detects whether input is

radiance or reflectance

• All in‐scene algorithms available w/ optional dark object subtraction pre‐processing

• If in ENVI 4.6, QUAC available

• FLAASH also available– Parameters auto‐populated to extent

possible (near complete for ARTEMIS NITF)

• Option to compare results from multiple algorithms side‐by‐side


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Contrast Enhancement ‐Dimensionality Reduction

• Reducing dimensionality may speed up processing and improve accuracy

• Image Transforms– ICA, PCA, & MNF

• Automated Band Selection– BandMax & Advanced Signature

Optimization

• Manual Band Selection

• Graphical subsetting tool streamlines review of bands


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The THOR Viewer

• ELT type viewer for ENVI

• Allows panning, zooming, rotating on‐the‐fly

• THOR adds target detection functionality

• Combines multiple decision planes into single layer for analyst


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Rule Thresholding

• One target overlay is generated per target

• Each overlay is generated by combining a user‐specified set of rule images


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Combining Rule Images


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• Pop‐up bubbles provide additional context for selected targets– Image chip shows corresponding area on ancillary image

– Spectral plot shows reference target signature and mean spectrum for selected target

– Additional info includes target name, area, and confidence rating for detection

Rule Pop‐Up Windows


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Stressed Vegetation Module

• Uses ENVI’s Vegetation Analysis tools, including 27 indices and three analytical products


envi training - goozmo, boulder colorado company · 1 envi training itt visual information...

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