ISWS - Hypoxia: Satellite Imagery of the Influence of Mississippi River Water...

Hypoxia in the Gulf of Mexico

Tutorial on Image Interpretation

Comprehensive 2002 Satellite Imagery Animation

2002, Quarter 1

2002, Quarter 2

2002, Quarter 3

2002, Quarter 4

True Color Satellite Image Tutorial Most true color satellite images in the 365-day 2002 satellite imagery series are of less than optimal quality for photo interpretation due to cloud cover, haze, glare, and/or just inherently poor differentiation of water color, such as occurs during periods of low river flow during calm weather. This short series of true color images provides the viewer with experience to interpret the 2002 true color imagery and its supplementary imagery.
	January 3 - Clouds obscure the main stream of the east-flowing boundary current, but the image shows interaction of the Boundary Current with Atchafalaya runoff and blockage of Mississippi water moving to the southwest. There is westward leakage of the Atchafalaya mud stream to offshore-flowing rivers by the Texas border. Outflow from the Terrebonne and Barataria estuaries, Atchafalaya River, Mississippi River, and inflow of offshore Gulf water form a four-way convergence over the Mississippi Trough. Outflow from the various Mississippi River outlets moves in various directions. [See SST counterpart]
	January 7 - Clouds partially obscure the main stream of the Boundary Current and outflows from the Mississippi River. Additionally, other than the deep blues, colors are not as brilliant. Otherwise, the same pattern occurs as seen January 3. [See SST counterpart]
	February 14 - A clear view of a largely three-way convergence over the Mississippi Trough includes outflow from western passes of the Mississippi’s landbridge. Some Mississippi River water moves offshore and east from the converge. Otherwise, the same interactions occur as in previous images. [See SST and chlorophyll counterparts]
	May 22 - Differentiation of water color has diminished. Nevertheless, four-way convergence over the Mississippi Trough is apparent, as is eastward movement of water away the eastern side of the Mississippi. Most Atchafalaya River water is moving west. [See SST and chlorophyll counterparts]
	July 17 - The Boundary Current is strongest during the warm months. Unfortunately it is also a time of difficult viewing in true color. Differentiation of water color is typically weak; strong warm weather convection creates frequent cloudiness and the high angle of the sun creates glare problems. The western half of the image is blanked out glare and blue and light greens are the visible water colors of the remainder. Nevertheless, the Boundary Current and nearshore current eastward summertime flow are now so strong that all visible water movement is from west-to-east both along the shoreline and offshore. [See chlorophyll counterpart]
	September 11 - Relatively faded color differentiation indicates at least three-way convergence over the Mississippi Trough and transport of some Mississippi River offshore [See chlorophyll counterpart]
	October 15 A — Colors are now stronger with autumn. Cloud cover partially obscures convergence over the Mississippi Trough (blue, green, and yellow seen through breaks in cloud cover). Interaction of the Boundary Current with Atchafalaya/shelf area and westward movement of the Atchafalaya mud stream to Texas rivers are clearly visible.
	B — This larger view of the northwestern Gulf of Mexico shows more of the Boundary Current.
	November 10: A — Strong eastward flow of the Boundary Current and nearshore current is greatest but not limited to warm months, as is shown here in this 1-km resolution image.
	B — This 250-m resolution image shows the head of the Mississippi Trough, nearshore current, outflow from Barataria Bay, and outflows from the various outlets of the Mississippi River.
Sea Surface Temperature (SST) Image Tutorial This short series of SST images provides the viewer with experience to interpret the 2002 SST imagery and its supplementary imagery. There are more SST images than true color images. True color images require daylight and SST images are taken day and night. Thus, there are SST images available when there are no true color images and some SST images may be of better quality than corresponding true color images.
	January 3 - This image supports the interpretation of its corresponding true color image. Additionally, it appears that eastward flow of water presses into the land bridge built by the Mississippi River and enhances the flow of water through passes on the other side of the land bridge. Using this January 3 image, reexamination of the January 8 SST image shows its less visually apparent manifestation.
	January 7 - This clearer SST image supports the interpretation of its corresponding true color image.
	February 14 - This image supports the interpretation of its corresponding true color image.
	May 22 - By this time of year, the range of water temperatures of river, estuary, and Gulf water has diminished greatly and warm-weather SST images are rarely used in the 365-day image set. However, May 22 river water is slightly colder than Gulf water. Although not used in the 365-day set, what this SST image does show supports the true color image. Additionally, there appears to be enhanced flow of water through passes on the East side of the land bridge like that seen January 3. Enhanced flow through the east passes of the land bridge are seen easily in higher resolution SST and reflectance images of the Mississippi available from the Louisiana State University website and referenced in the 365-day image set.
	July 17 - This warm weather SST image illustrates the major impact of clouds on daytime SST — as can be seen by the SST’s associated with a line of offshore clouds barely visible in the true color image counterpart. Although this complex SST image is not used in the 365-day image set, an SST pattern coincident with true color imagery indicates clockwise circulation in Terrebonne Bay and eastward (clockwise near-shore circulation) along the adjacent coast and the Mississippi’s land bridge.
	September 11 - This warm weather SST image has no major features relating to its corresponding true color and chlorophyll images.
	October 15 - A greater temperature gradient comes with autumn. Shown here is eastward deflection of much of the Atchafalaya/shelf area.
Chlorophyll Image Tutorial This short series of chlorophyll images provides the viewer with experience to interpret the 2002 chlorophyll imagery and its supplementary imagery. Because the 9-km resolution images are taken by a different satellite, there may be chlorophyll images available when there are no true color or SST images. True color, SST, and reflectance images presented here are 1-km, or better, resolution, and chlorophyll images either 9-km or 4-km resolution. Nevertheless, chlorophyll images are useful in supplementing and in interpreting other images and chlorophyll imagery traces water flow not discernible by the other three types of imagery presented here. Chlorophyll images are especially important in warm months when viewing by true color and SST are most difficult.
	February 14 - Convergence shows as just an indentation in chlorophyll-rich coastal waters in this 9-km resolution image. This chlorophyll image strongly shows offshore transport Mississippi River water but weakly seen in its corresponding SST and true color images.
	May 22 - Convergence shows as just an indentation in chlorophyll-rich coastal waters in this 9-km resolution image. This chlorophyll image shows the eastward flow of Mississippi River water more strongly than its corresponding SST and true color images.
	July 17 - This 4-km image supports the mass eastward movement of water seen in its true color counterpart.
	September 11 - This 4-km image shows eastward flow of the Boundary Current, which is interrupted and drawn inshore by inflow of offshore, low-chlorophyll Gulf water. Offshore flow of Mississippi River water is indicated just to the west of the inflow over the Mississippi Trough.
	Reference Beer, T. 1997. Environmental Oceanography. Second Edition. CRC Press, Boca Raton, Florida. 367 pp. Krug, E.C. 2006. Coastal change and hypoxia in the northern Gulf of Mexico. Hytdrology and Earth System Sciences (in Press).