This final page concentrates on various floods that were well monitored by space sensors.
Mapping the Extent of Flooding
This kind of information was a factor in predicting the major flood in the northern Midwest, late in the Spring of 1997. Satellite imaging gave a critical look at the great floods on the Red River in North Dakota and Manitoba (Canada) that inundated Grand Forks, Fargo, and other towns along the state's border with Minnesota.
Spring flooding is frequent in parts of the Mississippi River basin. A hundred-year flood, i.e., largest expected statistically in a 100-yr span, resulted from snow melt and rain in late March of 1973. This Landsat-1 subimage (with an earlier pre-flood view), captured the extent of flooding on a cloud-free day, showing St. Louis, Missouri (protected from downtown flooding), and the flood plains of the Mississippi, Missouri (joined at A), and Illinois (at B) rivers: Twenty years later, the Midwest again flooded, worse than before, in fact many places recorded the highest flood levels in their history. After several months of excessive rain that saturated the soil, because of a blocking high pressure system that kept the jet stream relatively stationary, in late July and August of 1993, water levels rose well above flood stage. Areas hardest hit were from Iowa to southern Illinois. Levees broke, inundating tens of thousands of acres. The '93 flood, said to be largest ever on the Mississippi, became the costliest in U.S. history (some estimates approach $15 billion). Satellite imaging played a key role in getting a number of good images of the flooded area.
Once again we examine the lowlands northwest of St. Louis. First is this Landsat image:
The next image was taken by Shuttle astronauts, using SIR-C radar. (Note that the orientation has west near the top.) Below that is an image of merged JERS-1 radar and a SPOT 3-band composite, which offers considerable detail (notice how farmlands show through the water). 14-41: Which year does the Mississippi flood seem worse? Why isn't St. Louis flooded? ANSWER The flooding of 1993 affected many rivers. Floods occur as early as June and as late as October (see this NOAA website for an historical review). The next three photos show the flooding at St. Louis (on August 1 the flood peaked at the waterfront at 49.6 ft, 19 feet above flood stage and 6 feet higher than during the 1973 flood shown above), Jefferson City, MO, and Alton, IL: Up river during the same 1993 flood, the SAR radar on ERS-2 rendered the flood in mostly black tones in this scene near Dubuque in southeast Iowa:
The effects of the 1993 persisted in the lowlands near St. Louis well into 1994, as indicated by this March 1994 photo taken from the Space Shuttle:
Flooding can occur anywhere on all continents except the Antarctic. The next image is a Landsat-1 subscene (February 6, 1974) of the Barcoo River in Queensland/South Australia, flooded by Fall rains. The floodwaters have spread greater than 50 km (31 mi) wide in these low-lying plains, with low rolling hills.
The Yangtse River in China underwent a major flood in August of 1998. Millions were driven from their lowlands homes. This Radarsat image shows the flooded lands near Wuhan:
In this unusual image, an ERS-1 radar image taken during June of 1993 is joined with an ERS-2 radar image taken on August 1, 1998, providing a multitemporal or change detection rendition. Both blue and red associate with flood waters.
Radar is especially powerful in recognizing floodwater extent since the low reflectivity from water makes it appear dark. Floods can be beneficial as well as harmful. These two Radarsat images show annual flooding in the Mekong River basin in Cambodia. Waters from the monsoon rains collect in the basin and replenish the ubiquitous rice paddies that provide the main food supply for the Vietnamese and Cambodians.
The pair of MODIS images below show parts of Namibia, Botswana, Zambia and Zimbabwe in which the rivers are normal and then in flood:
Finally, check this map showing areas with high soil moisture, a condition that bespeaks of water saturation from earlier heavy rainfall or from previous flooding. This soil wetness map shows much of Asia; maps of all the continents plotting this parameter are made by NOAA/NESDIS.
This lengthy Section 14 purports to convey that the principal use of remote sensing remains surveillance of weather systems and oceans on local-to-global scales. We report this because of the widespread occurrence of water on the Earth's surface (even greater than the 70+% ocean surface area, stated on page 14-1, if we include the Antarctic ice [which stores more than 80% of the world's {frozen} fresh water] and Greenland.
At this point in the Tutorial, we have examined most of the specialized modes of remote sensing (defined by the electromagnetic spectral regions we can use), the spacecraft systems that mount the sensors, and the numerous applications to which these sensors have contributed. In the next Section (15), on Geographic Information Systems (GIS), we look at some systematic ways to integrate remote sensing data into organization, correlation, interpretation, and management of geographically-referenced information. Then, in Section 16, we look ahead to some of the current or recent remote sensing programs, in which individual satellites will simultaneously make meteorological, oceanographic, land surface, and biologic observations to present a unified picture of Earth as a System.
Primary Author: Nicholas M. Short, Sr.