# Presentation: 774255

## Slide 1

**Notes:**
A source (node #3 - the blue star) is placed in the northwest quadrant of this urban domain and site 28 (the green square) is highlighted in the center east region of the domain.  The “Footprint” display for the source and the upwind “Danger Zone” display for the site have been captured from an interactive, real-time CT-AnalystTM assessment.  The wind is from the north north east (15 degrees) at 3m/sec.  The salmon (light red) shaded footprint shows the limiting contamination region (after half an hour or so) resulting after a large source has been released at the indicated location.   All points within this footprint have a significant likelihood of being contaminated beyond tolerable limits during the indicated time interval by a large source.  However, at any particular time the air at a particular point may be devoid of contaminant.  
      The check boxes in the lower right region of the window control the displays activated.  A wide range of display overlaps and combinations are possible depending on  the situation and the data analysis required.  CT-Analyst deals with a number of node locations that are moveable on a map.  The Dispersion NomographTM tables that power CT-Analyst contain all the 3D flow data governing contaminant transport (CT) in the region displayed.  Scenarios are constructed by moving the nodes marking sites, sensor reports, and inferred or observed source locations around the map and selecting subsets of those nodes shown for inclusion in the display computations.  The triangles are “automatic” sensor nodes, red indicating that a contaminant has been detected at that location and “blue” indicating that there is no contaminant at the point.  Green squares are sites that could be leaking contaminant or at which a meeting will be held and for which special precautions are required.  The star nodes are sources.  We may not initially know a source’s location so a manual/remote sensor mode is provided to allow backtrack to unknown source locations and the utilization of anecdotal and qualitative data. 

## Slide 2

**Notes:**
An inferred source location has been identified by CT-AnalystTM marked by the black star in the Northwest quadrant of this domain.  Knowing even an approximate source location and properties is not necessary a priori because CT-Analyst can backtrack to an unknown source location from point measurements.  The wind is now from the west north west (295 degrees) at 4 m/sec.  The sensor fusion “Backtrack” display that determines the source location is shown.  The upwind V-shaped, turquoise-shaded regions show where sources could activate the hot sensors (red circles).  The darker areas show where these upwind source regions from the four selected “hot” sensors overlap. This multi-sensor fusion operation automatically bounds the lateral location of the suspected source.  The two solid blue “cold” sensors near the selected “hot” sensors have not detected any contaminant and can be used to limit the possible source region upwind. The dark blue region around the inferred source node is where the source will be most likely found.  This determination can be made in 3 to 5 minutes with no source node present if the sensor readings are inserted manually or collected over the network - as permitted by CT-Analyst.
        A downwind “Consequence” region, the likely contamination region, is shown by the mustard green shaded area.  This area is the composite result of contaminant detected as it passes the four active “hot” sensors.   The consequence region can be used to initiate consequence management, i.e. evacuation and closing down buildings, even before the source location is inferred reliably.  Because the sensor spacing is finite, a city block or so in this example, there will always be contamination outside the consequence region untiol the source is backtracked.  Unfortunately a limited number of sensor readings cannot define this strip directly.  In actual use, of course, one would be unlikely to know the source location.  Therefore CT-Analyst permits the option of external (manual or network) setting of all the sensor readings.  Both fixed site and mobile sensors can be accommodated.

## Slide 3

**Notes:**
An inferred source location is marked by an active source node after the sensor fusion backtrack procedure shown in Figure 2. The wind is again from the west north west (295 degrees at 4 m/sec). The “Plume Envelope” display now replaces the interim “Consequence” display once a source location has been inferred. The salmon (light red) shaded area shows the currently contaminated plume envelope at 5 minutes after release. The asymptotic “Footprint” display outside the current plume envelope is gray when the time-dependent plume envelope is activated within it, indicating the overall region that can become contaminated if the source is large enough  (something we are unlikely to know in the first few minutes of an  incident). All points within this plume envelope have a significant likelihood of being contaminated beyond tolerable limits during the indicated interval.  Because different realizations of the same scenario, varying in specific wind fluctuations and phases of building vortex shedding, will have somewhat different plumes, the CT-AnalystTM displays are designed to bound these realizations in an accurate but conservative manner. The trade-off between these two qualities is addressed through quantitative Figures of Merit elsewhere. 
      Note that the plume envelope must be activated in conjunction with the footprint  so both are shown superimposed.  When the “Simulation” box is checked, the time line is activated.  The plume envelope evolves in a time-like manner, moving between and around buildings, and expands laterally as well as downwind, etc.  This appearance is deceiving because no integration is being performed - accounting for the “zero-latency” feature.  Using the + and - controls, CT-Analyst can advance the plume at 1X, 10X, 100X, 1000X and 10,000X times real time.  The slider for the time can also be positioned manually and even moved backward.  The plume envelope can also be set for a particular time after release and all the other parameters changed such as wind speed, direction, source location, etc. in mid scenario.  

## Slide 4

**Notes:**
The source location inferred graphically by CT-Analyst in the previous two figures has been moved slightly to the west in Figure 4 (about 40 or 50 meters) and the “Plume Envelope”, “Footprint”, and “Escape” displays have been activated interactively - along with the” Backtrack” display.  Source node has been activated, as shown by the blue star at the new inferred source location above, and the plume envelope is displayed 20 minutes after contaminant release.  The wind is still from the west north west (295 degrees at 4 m/sec). Although the plume envelope fills a yet  contaminated.
      Notice that the upwind edge of the gray footprint in the center of the region now follows the re-circulation zone of a large building about 200 meters further to the west than the building establishing the edge of the footprint in Figure 3. This illustrates the great sensitivity that the plume envelope and footprint have to source location in some regions.  There is a corresponding insensitivity in others. Also note that the plume envelope has not yet reached this location.  Sometimes different sensor reports will have to be used for the backtrack because of this sensitivity.  Sensors near the edges of the plume more narrowly define a possible source region but they may also change their reading late in time as a result of slight expansions of the plume actually being detected.
       CT-Analyst can be run as a simulation by placing the cursor at the right end of the time slider and holding the left mouse-click down.  The “simulation” advances up to 10,000 times real time.  Alternately the slider can be simply dragged to the correct time, either forward or backward.  Because the nomograph influence matrix has been carefully computed ahead of time using 3D, time-accurate CFD simulations, accuracy does not suffer to provide this speed.  As computers become more and more powerful, the quality and resolution of the tables can be improved, meaning that this overall approach is also fully convergent without loss of speed.

## Slide 5

**Notes:**
Two or more distinct sources can be inferred in a single Backtrack operation as seen in this composite “Backtrack” display.  The Plume Envelopes are displayed over the composite contamination Footprint 7 minutes after the sources were released.  Note that the upper (northward) source plume envelope is beginning to wrap around one building in the center of the screen but the gray Footprint indicates the contaminant will eventually move much further west (upwind) as indicated explicitly in Figure 4.
      The upwind V shaped blue/violet/dark blue shaded areas show the regions upwind of  the active ‘hot’ (red) sensors where a source would have to be located to activate the particular sensors.  The darker areas show the regions of overlap of these possible source regions and bound the cross-wind localization of the inferred source.  The blue-colored ‘cold’ sensors at the ends of this line of sensors have not detected any contaminant as yet.  Their information  further localizes the source by excluding large upwind areas where the source can not be expected to be found.  The turquoise colored upwind exclusion areas from these sensors is also shown automatically in the Backtrack display.
      The Backtrack function activated for this display is automatically initiated when the control button is clicked (checked) but the result depends on the instantaneous state of all the other nodes and elements of the CT-Analyst system.  All sensors potentially enter the assessment as well as the wind speed and direction (295 degrees and 4 m/s here) and the geometry of all the buildings, trees and terrain.  Correctly using the urban geometry is also crucial to making “false alarm” determinations.   The Backtrack capability is equally valid and effective when no source is present.  Then the state of each sensor is determined externally and updated either through the graphical interface or by connections to network sockets.  Autonomous mobile sensors can be incorporated since a CT-Analyst node or set of nodes can be slaved to a communications down link from each separate sensor.