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Introduction
The MISR and MODIS instruments aboard the Terra satellite produce a number of parameters relevant to the study of wildfire smoke plumes. This website is a publicly-available repository for the data acquired by MISR and MODIS and processed under the auspices of a project to develop an aerosol injection height climatology to support wild fire, climate change and air quality studies. The project is funded by the EPA and NASA and includes investigators from JPL, Harvard University, University of California at Irvine, University of Michigan and Washington State University.
One of the MISR team's contributions to this project is to provide a database of information on smoke plumes extracted from the satellite data sets that includes the location and time of plume observations, plume height measurements (from which injection heights may be deduced), the approximate radiative power of their associated fires, the direction of transport of plumes, the areas of individual smoke plumes, and aerosol properties and albedo estimates. In this context, smoke plumes are considered to be discrete regions of smoke that can be traced to their fire sources at ground level and that have a distinctive shape determined by the direction the smoke is driven by the wind. Similar information is retrieved for selected regions of dense smoke not clearly associated with specific fire sources (smoke clouds), and whose direction of transport is not easily determined.
The acquisition of these data is accomplished using an interactive visualization program named MINX which allows users to manually digitize plumes and other features (which together are termed regions) and to compute smoke height and wind velocity using a new stereo height algorithm. The program automatically creates the imagery and raw data files described in this document. The MINX program and its documentation can be freely downloaded from the Open Channel Foundation website at http://www.openchannelsoftware.org/.
Specific MISR products used by MINX in constructing this data collection are the ancillary AGP product containing the MISR digital elevation data, and the following standard products: level 1 terrain-referenced radiances, level 1 geometric parameters, level 2 scene classifiers and level 2 aerosol. The single MODIS product used is the Level 2 MOD14 Thermal Anomalies product from the TERRA satellite at a resolution of 1 km.
Website Organization
At the top level, the main page is organized by project area and date. The first project area studied was Alaska and part of the Yukon Territory, Canada, for four months in mid-2004, due to the unusually large numbers of fires during that season. The 2002 fire season for all of North America was studied next, and North America for 2006 is expected to follow.
To go to a project area, click a View/Download link in the Images and Data column. The project page that appears contains an index map showing the location of all the plumes in the project, a list containing basic plume statistics for the project area, three links that are described in greater detail below and a table of MISR orbits and block ranges where smoke plumes were found, together with the date the MISR data were acquired and the number of plumes found in each orbit and block range.
Ten-day Plume Statistics
When you click on this link, you will see a table that summarizes important plume characteristics for the project in histogram fashion by ten-day intervals. For each ten-day period, these parameters are enumerated: number of plumes, median height of plumes above sea level, mean area and mean power.
Project Summary Files
This link takes you to a page from which you can select to view the summary file either for digitized smoke plumes or for digitized smoke clouds. These files are constructed during a post-digitizing pass that reads smoke plume and smoke cloud raw data files for all digitized regions and compiles the summary information.
Clicking on either link brings up an ASCII text file containing up to 56 columns of data with one smoke plume or smoke region per line. There is an extensive header at the top of these files that describes each data column in detail. The smoke plume or cloud heights in these files (column 16) are median values estimated from the many raw data points in each plume. You may decide that using raw data points instead gives you better control over the application of these data to your work.
If you wish to download one of these summary files, simply right-click in the data page and select the Save Page As… option from the mouse menu. In the SaveAs dialog box that appears, specify the location to which the file should be saved and click Save.
Raw Data Files
If you click on this link, you are shown a page containing a large table consisting of eleven columns of information in which each row represents a single smoke plume, smoke cloud or area of clear land (regions). This table enables you to select those regions for which raw data files will be downloaded to your computer.
The first three columns of the table contain the components of the name of a digitized region: orbit number, block number and region type plus unique number. There are currently three region types, smoke plume (P), smoke cloud (S) and clear land (L). The Type/Number column has additional functionality - if you click the colored link in any row, you are taken directly to the images and data plots for that region (see descriptions below). Similarly, the View links in the Raw Data File column can be clicked to take you to the ASCII file containing raw data for that region.
You can click on the column name in the header of any of the first nine columns in the table, and the table will be sorted in ascending order by that parameter. This is helpful for selecting a subset of raw data files for downloading. The final column named Download File contains checkboxes that you should use to indicate which plumes you want to download. Alternatively, you can click the Check All button at the bottom of the table to select all rows.
An Advanced Search link is also available above the right edge of the table. Clicking this opens a filter panel that allows you to specify the minimum and maximum values you want to include in your search for each of five parameters. Once you have done this and have clicked the Submit Advanced Search button, the table is updated to include only those rows that satisfy your search request. Next check the boxes in those rows corresponding to regions you want to download or click the Check All button at the bottom of the table to select all rows.
Once you have made your final selections, click the Review File Selections button to review them. This page also has a box at the bottom for entering your email address. Enter your address here, and press the Email List of Selections button, and a file will be sent to you that contains information you will need for pulling the files down to your computer.
When the email arrives, click on the link in the email that describes the "curl" application and follow the directions it provides. You can see the same information by clicking the Download Help link on the page where you enter your email address.
Orbits/Block Ranges Table
Clicking on any colored link in the Orbits/Block Ranges column of this table on the project page brings you to the Region page for the appropriate MISR orbit and block range in the project. This page gives you access to the images and plots captured during the digitizing process. An index map in the upper left corner displays the location of all the digitized regions as well as the MISR block outlines. The table at the bottom lists those regions together with four additional parameters for each. The columns are:
- Region Name - The unique name assigned to the region. This includes the orbit number, the block number, a letter designating the type of region (smoke plume, smoke cloud or clear land) and a unique number in the orbit and block.
- Region Type - The long word description of the region type.
- Height - The estimated median height in kilometers of points representing the top surface of the smoke plume or cloud.
- Direction - The angle in degrees measured clock-wise from north corresponding to the direction in which the plume smoke is being blown.
- Total Power - The total radiative power in megawatts of the plume as estimated from the MODIS MOD14 product (this is the sum of the radiative power in all MODIS pixels captured for this plume during digitizing).
Clicking a colored link in the Region Name column on the Plumes page displays the individual region data page for the selected region. Each of these pages contains15 images and plots for the region as well as a link at the top labeled View/Download Raw Data. Using this link, you can obtain the raw digitized data used in constructing the plots for any plume or smoke region. Alternatively, you could use the Raw Data Files link on the project page. There are also Previous Region and Next Region links at the top left and top right of this page that allow you to navigate directly between the images for different plumes in the same orbit.
Image Description
Maps
Index maps are provided at each level of the website below the main page. At the individual region level, the map shows only the current region and the MISR block outline. On all the maps, smoke plumes are indicated in red, dispersed smoke clouds are indicated in blue and clear land regions are shown in green.
MISR Images
Two MISR nadir camera images (An) are shown on each page with the same scene but different overlays. The first image has overlays of the digitized region outline and name in green (smoke plumes) or aqua (smoke clouds) or yellow (clear land). An arrow indicating the wind direction, as interpreted by the digitizing operator, is drawn in yellow. MODIS thermal anomaly pixels are drawn as red dots.
The second nadir image shows a color-coded dot posted at each successful wind-corrected, height-retrieval point inside the current plume or smoke region. The color key with which to convert the colors to heights is shown on the image. An arrow indicating the wind direction is drawn in yellow.
MISR Animation
The MPEG camera animation of the region allows you to view MISR's nine camera images in succession in order to visualize the 3D nature of the plumes and to view the differences in scene reflectance and the effect of differences in atmospheric travel path at different viewing angles.
The best way to view the nine camera images is by grabbing the manual control using your mouse and moving the control back-and-forth. Since these are MISR terrain-referenced images, you will see patches of black pixels appearing on the more oblique-looking camera images in mountainous regions. These are effectively no-data, shadow zones created when images are re-projected from the ellipsoid to the terrain.
Height Profiles
Height profiles are constructed by sorting heights successfully retrieved for a region, by increasing distance from the first point digitized. For smoke plumes, the first point digitized is always near the smoke source on the ground where there is live fire. For dispersed smoke regions, the first point digitized is selected at random. The wider the region digitized, the more points there will be at a similar distance from the source. These will be represented on the profile as different heights at the same distance coordinate creating the appearance of a poorly defined plume top. It is important to study the color-coded An height image to understand the 2D spatial distribution of heights as well as the 1D distribution that the profile represents. For the terrain height profile, the appearance of a saw-tooth pattern that this 1D representation sometimes causes can be disconcerting.
Height profiles for smoke plumes show the terrain height as a green line, plume heights un-corrected for wind (zero-wind heights) as red X's and heights corrected for wind as blue squares. There are typically fewer wind-corrected heights than zero-wind heights.
When there are at least four successful wind-corrected heights for a plume, then two estimates of height are attempted. Both are based on fitting a plane to the heights, then removing all points more than 1.5 standard deviations from the plane. The Maximum Height Estimate is the maximum height value that remains, and the Median Height Estimate is the median value of the remaining point heights. Raw data files for each plume are accessible from the website so independent calculations of standard heights can be made.
For dispersed smoke regions, there is no wind retrieval, so there can be no wind-corrected heights. The Maximum and Median heights are calculated as above but represent zero-wind heights.
Wind Profiles
Wind profiles share a distance axis with height profiles, and they split the wind-speed vector into across-track (red) and along-track (blue) components. Positive wind-speeds are defined to be toward the north (i.e. up-track) and toward the east (i.e. toward the right of the track). Unless there is a successful wind retrieval for a point, there cannot be a wind-corrected height.
Note that if there is a component of wind in the along-track direction toward the south (negative), then the corrected height will be greater than the zero-wind height. If there is a component of wind in the along-track direction toward the north (positive), then the corrected height will be less than the zero-wind height.
Wind retrievals and wind-corrected heights are less reliable the more the wind direction is aligned with the MISR along-track direction, because the along-track component of satellite motion becomes inseparable from the along-track motion of the smoke. For plumes that are closely aligned with the along-track direction and have wind-corrected heights with much greater scatter than the zero-wind heights, the wind-corrected heights should be used with caution.
Height and Wind Histograms
For smoke plumes, four histograms summarize the height and wind data, two for zero-wind and wind-corrected heights and two for cross-track and along-track winds. These histograms are computed from the points plotted on the height and wind plots. For smoke regions, there is only a zero-wind histogram, since no wind retrieval is performed.
Albedo Profile
Albedo profiles also share a distance axis with height profiles. Spectral albedos are calculated at the Top of Atmosphere (TOA) during plume processing by MINX rather than read from the MISR level 2 products, because of resolution and algorithm considerations.
The spectral albedo algorithm is similar to that used in the MISR TOA local albedo product, but it differs in several respects. First, rather than re-projecting the radiances for each camera to the tops and sides of rectangular prisms that represent cloud heights, the disparities from the camera-matching step are used to co-register pixels from the same part of the scene for each camera. Second, the total radiances at these pixels are used in the solid-angle weighting calculation, whereas in the local albedo product, only the radiances projected to the tops of prisms are used. Finally, plume albedos are calculated at 275-meter resolution, whereas the local albedo product computes albedos at 2200 meters resolution.
Aerosol Histograms
Aerosol data are read from the MISR standard aerosol product. They are reported at 17.6 km resolution and are typically not available when the optical depth is very high or when there is cloud contamination. When aerosol results are retrieved by MINX, it is usually because a low optical depth region of smoke is present near the plume being digitized.
Because the low resolution of the aerosol product sometimes results in an entire plume being contained in a single aerosol pixel, histograms are not the best way to represent these data. A different method for representing them may be implemented in the future.
Two of the histograms, "Optical Depth" and "Single-Scatter Albedo", contain spectral data. The colors of their bars correspond to the spectral bands they represent. On these histograms, when more than one band occupies the same Tau or SSA interval, the bars are drawn with the largest value in the back and the smallest in the front to make all the bars visible.
The "Tau Fraction by Particle-Type" histogram depicts the fraction of the green-band optical depth value that is attributable to small, medium and large particle sizes. The weighted sum of these fractions must equal 1. The histogram also shows the fraction of the green-band optical depth value that is attributable to spherical particles. The non-spherical fraction is not shown and is simply 1 - spherical fraction. This histogram also has a key that identifies the meaning of its colors.
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