December 9, 2004

Understanding the images

This special post presents brief descriptions of maps and images often used on the Smog Blog. We hope that they will help you better understand the products. For comments and suggestions on making each visit more enjoyable, please contact us.

University of Wisconsin-Madison Red Green Blue MODIS Image Products

RGB MODIS images are developed by the Space Science and Engineering Center (SSEC ) team at the University of Wisconsin-Madison. The true color images are generated from information given by the MODIS instrument aboard the Terra and the Aqua satellites. MODIS provides a variety of nighttime and daytime products such as Cloud Top Pressure , Total Precipitable Water Vapor, and Vegetation Cover Conversion.

This is a true color image of the US with parts of Canada and Mexico. This particular image was taken by MODIS on Terra, which is a polar orbiting satellite.
The surface outside the sensor Field Of View (FOV) is black (1). Coast and state lines have been added for geographic reference. Blue regions are water bodies (2). White surfaces could be clouds or haze. (3) is a cloud and (4) is haze which is thinner and grayer than clouds. South of Louisiana, the water is tinted with an orange like color caused by run off pollution from the Mississippi River or organic material (5). This phenomenon should not be confused with sun glint (6) which is the reflection of the sun off the water.

The fair blue color (7) is due to the presence of different algae and micro organisms. The variation of land color (8) is due to the difference in vegetation coverage . Dark green is for heavily forested regions and yellow is for drier zones. The grayish color in the top right corner of the image is smoke (9), in this particular case, coming from the Alaska and British Columbia fires . It may be difficult to distinguish smoke from haze on a true color image. However, smoke is transparent on a band 04, 07, 07 image. Comparing photographs A and B taken July 8th 2004, the smoke is visible on photograph A but invisible on photograph B.

Photograph APhotograph B

The top of the picture has the name of the sensor, the date (yyyy-mm-dd), the path starting and ending time in UTC military style, the bands used and the region.

For more information on MODIS go to MODIS Web . For MODIS images go to MODIS Direct Broadcast at SSEC . Comment concerning this particular image can be obtained on the Smog Blog site.

Regional plots of MODIS Aerosol Optical Depth, tau and Cloud Optical Thickness Product

This map was generated from MODIS Terra data, by the Infusing Satellite Data into Environmental Applications (IDEA) team, a partnership between NASA, EPA and NOAA.

This image shows the Aerosol Optical Depth (AOD), the cloud coverage and the in-situ PM2.5 monitors in northeastern US. This map represents the EPA region 5.

At the top of the map resides a description of the product name, the date (yyyy mm dd) and the Environment Protection Agency region number (1). At the bottom, the first color bar represents the Aerosol Optical Depth values and the second is for the Cloud Optical Thickness (COT) index. Black surfaces are regions with no available data (2) and white dots are the PM2.5 monitoring sites (3). In the presence of clouds, there is no AOD data. Longitude and latitude are in dotted lines while the coast and state lines are in plain white.

For more information concerning IDEA and its products, go to the IDEAwebsite. For comments concerning this particular image go to the Smog Blog post .

Source: IDEA date accessed 08-27-04

GOES Aerosol/Smoke Product (GASP)

GASP images are developed by NOAA-NESDIS and are generated from information given by the two GOES geosynchronous orbiting satellites.

The top of the picture (1) has the product name, the Coordinated Universal Time and the date (m/d/yy). To calculate Eastern Standard Time, do UTC - 4 for military time and UTC - 16 for 12-hour time after 1pm. The color bar at the bottom represents the AOD level. Regions with higher particle concentration have a higher AOD (2). Clouds and haze are in white and gray (3). Coast and state lines are in black.

For more information on GASP images and products, go to GASP website. For comment on this particular image see Smog Blog post

Current AQI ? Particle Pollution (PM2.5)

This product is generated by the Environmental Protection Agency (EPA) in an effort to monitor the air quality (AQ) in the U.S. The map can be static or dynamic.

Each circle represents a monitoring site (1). The EPA uses a six-color code to classify each site. The colors go from green, meaning "good" Air Quality Index with PM2.5 level up to 15.4 ug/m3 (AQI), to maroon, standing for “hazardous” (250.5 ug/m3 and more). Gray circles (2) are sites with no available data.

To obtain this product and for information on other products such as main pollutants and ozone index click here. For comment concerning this particular map see Smog Blog post.

Source: EPA AIRNow date accessed 08-26-04

MODIS Rapid Response System MODIS RGB Image

These maps are generated from MODIS data on Terra and Aqua. These images are not reprojected, therefore they are very distorted at the swath edges. This particular image comes from the Aqua satellite.

This is a true color image of southeastern U.S. (1) Blue lines are longitude and latitude lines. Clouds and haze are in white and gray. The yellowish color is caused by sunglint (2). Fires are represented by red pixels (3). Each dot does not correspond to the actual size of the fire. It could be a single fire or multiple fires that cause the pixel to be flagged as fire pixel. The small globe (1) with the satellite name, date and time information (4) was added to the map while being posted on the Smog Blog. The date format is as follows: yyyy / Julian date mm/dd/yy. The time is in Coordinate Universal Time. For additional explanation see “University of Wisconsin-Madison Red Green Blue MODIS Image Products”.

To obtain similar images go to Rapid Fire.
For more comments concerning this particular image see Smog Blog post.

Hazard Mapping System Fire and Smoke Product

The HMS product is generated by NOAA-NESDIS from various data obtained from MODIS, GOES AVHRR and DMSP/OLS images. The HMS map allows the user to visualize the points of fire as well as smoke plumes.

The following is a description of this particular HMS map. The American and Canadian coast and state lines are in green. The red pixels are detected fires (1). Notice that the fire may actually be smaller than represented here. The gray surfaces are smoke plumes (2). Note that this map is generated from models and algorithms and is not always accurate. However it gives a good representation of major smoke plumes.

For more information on HMS maps visit the HMS website. For additional comment regarding this particular map visit the post Smog Blog.

HDFLook Generated MODIS AOD Map


This map is generated from MODIS Terra data by the UMBC Atmospheric Lidar group using HDFLook. Similar maps can be generated using MODIS Aqua data. The image shows the Aerosol Optical Depth (AOD) and the cloud coverage. The surface outside the sensor Field Of View (FOV) is white (1). Coast and state lines have been added for geographic reference. (2) represents the plume of aerosols. White surfaces are regions with no available data. The lack of data may be due to clouds (3). Sun glint (4), which is the reflection of the sun off the water, also makes the detection of aerosols difficult. The color scale has been adjusted to roughly approximate the EPA AQI six-color scale. This particular image is generated with July 26 2004 data.

For more information on HDFLook click here.

UMBC Polar ELF LIDAR product

LIDAR, or Light Detection And Ranging, is a remote sensing technique used to observe the height and the scattering properties of atmospheric constituents. Pulses of light are emitted into the atmosphere and the backscattered light is first collected with a telescope, and then measured. The time delay between emitting the pulse and receiving the signal gives the height at which the light was scattered. The amount of backscattered light is related to the number of particles at that height.

This image was generated from the Polar ELF LIDAR system data by the UMBC Atmospheric Lidar group using MATLAB.

The image above shows an example time series from July 20, 2004 taken at UMBC. The top of the picture has the starting and ending date/time (1) in Universal Time (UTC or Greenwich Mean Time). See GASP image description for UTC time conversion to EDT. The y-axis in this image is height, ranging from 0 km to 5 km. The x-axis is time. The color axis (2) reflects the amount of material involved in the light scattering and how well they scatter: blue being very clear with fewer particles, red being very hazy with more scatterers.

This image illustrates the ability of the lidar to observe the dynamics of the atmospheric boundary layer. Two plumes of aerosols aloft are indicated in this particular image. The first plume (3) moved over UMBC in the morning at an altitude ranging from 1 km to 2 km. The second plume (4) appeares in the evening at about 4 km to 5 km. Also evident in this time series is the convection of the boundary layer. This boundary layer is occasionally cloud-capped. In the morning, the majority of the particulate matter is concentrated near the surface (5), seen by the dark red colors. In response to the sunrise at 14:00 UTC, the boundary layer, in magenta, rises and aerosol convection is observed in this process. This leads to a well-mixed uniform boundary layer (6) in the afternoon. The dark blue vertical bands (7) above the clouds are similar to the shadow that clouds cast on the ground. However, these shadows are above the clouds due to the fact that the lidar is looking upwards and emitting the laser beam from the ground to the sky.

Posted by Kamonayi Mubenga at December 9, 2004 11:33 AM