Oscar K. Huh

Wetland Loss in World Deltas

Abstract Geologic and geomorphic data on 42 world deltas were compiled for a NASA-sponsored research project. Satellite images from 14 of these deltas (Danube, Ganges, Brahmaputra, Indus, Mahanadi, Mangoky, McKenzie, Mississippi, Niger, Nile, Shatt el Arab, Volga, Huang He [Yellow], Yukon, and Zambezi) were analyzed for delta plain wetland loss caused by natural causes and conversion of wetlands for agricultural and industrial use. These analyses indicated that a total of 15,845 km2 of wetlands have been irreversibly lost during the past 14 years and the average rate of loss is 95 km2/y. If a similar trend is present in the other deltas, a total wetland loss in the delta plains of the 42 deltas would be on the order 364,000 km2 over the past 15 to 20 years.

Study of river flood hydrology in Bangladesh with AVHRR data

Abstract This paper examines the applicability of NOAA satellite AVHRR imagery to monitoring and studying the river floods and associated hydrological conditions in Bangladesh and the adjoining regions. The flood period considered is that of the last 10 days of September 1984, when Bangladesh experienced one of the worst floods in recent years. Imagery from dry winter conditions have also been used for comparison. The analysis involved the calibration of the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) IB data tapes, linearization of pixel sizes and geometric rectification of the image to ground reference points. The imagery showed that a vast area of Bangladesh was flooded and rivers were highly turbid. Comparisons have been made between the major rivers, particularly the Ganges and the Brahmaputra, during the flood season. It has been found that the Ganges has higher albedo (is more turbid) and is warmer than the Brahmaputra during the flood season. The Brahmaputra shows a gradual increase in...

Thermal history of reef-associated environments during a record cold-air outbreak event

SummarySeveral polar continental air masses intruding into the south Florida/northern Bahama Bank region during January 1981 caused record low air temperatures and rapid chilling of extensive shallow-water carbonate systems. Numerous “coral kills” along the Florida reef tract and massive fish mortalities in Florida Bay were attributable to unusually cold waters generated at this time. Thermal evolution of Florida Bay/Florida reef tract and northern Bahama Bank waters from 8 to 21 January was assessed from thermal infrared data acquired by the NOAA-6 environmental satellite, in situ water temperatures, local meteorological data, and a computerized heat flux model. Field observations and laboratory experiments identify 16°C as a thermal stress threshold for most reef corals (Mayor 1915; Davis 1981). Temperaturecorrected digital satellite data indicated that water temperatures below 16°C were generated in Florida Bay and on Little and Great Bahama Banks during a 10-day period in January. Lowest temperatures on the Florida reef tract resulted from offshelf transport of Florida Bay water through major tidal channels. Offshelf movement of bay water is driven primarily by strong northerly winds, density gradients, and tidal pumping. Absence of reef development opposite major tidal passes along the Florida reef tract (Ginsburg and Shinn 1964) and aperiodic coral kills along bank margins can be attributed to this process, which has probably had a limiting influence on Holocene reef development in these areas.

Evolution and structure of a coastal squirt off the Mississippi River delta: Northern Gulf of Mexico

In early October 1992, satellite-derived sea surface temperature data revealed a 200 km long and 10- to 30-km-wide stream of cool water flowing toward the southwest from the Mississippi River delta region. Satellite imagery and in situ measurements have enabled a detailed study of the squirts kinematics and subsurface characteristics over a 2-week period. In its early stages, the squirt appeared as a narrow, high-speed (>75 cm/s) jet of water which flowed westward over the Mississippi Canyon, forcing a semi-submersible drilling rig to suspend operations from October 2 to 4. After crossing back onto the shelf, the squirt spread laterally, yielding a mushroom-shaped feature, 75 km wide, which consisted of counter-rotating vortices. Northeasterly wind forcing (averaging 10–15 m/s) and water level setup east of the delta appear to have been the primary mechanisms for evolution of the high-velocity currents. Satellite and in situ measurements demonstrate that the dipole eddy was comprised of a cool, low-salinity, low-density water mass at least 26 m deep in the center and 16 m deep along its margins. This event demonstrates that strong northeasterly winds over the northern Gulf of Mexico can initiate along-shelf and off-shelf flows of cooler coastal waters, contributing significantly to seasonal cooling and freshening of the continental shelf and to shelf/slope exchanges of water. During this event, approximately 100 km3 of inner shelf and river water was transported off the continental shelf, a volume equivalent to 17% of the average annual discharge of the Mississippi and Atchafalaya Rivers.

Fall-Season Patterns of Turbidity and Sediment Transport in the Korea Strait and Southeastern Yellow Sea

Abstract Suspended-sediment data collected in mid-November of 1980 and 1981 and current meter moorings deployed in September and early October of 1982 suggest an early-fall entrainment and subsequent transport of suspended sediment into the Korea Strait by the South Korean Coastal Current. During transition from summer to winter conditions, suspended-sediment concentrations in the southeastern Yellow Sea range from 5 to 100 mg/1 at the surface and 15 to 250 mg/1 at the bottom in waters that are 20–80 m deep. These concentrations, 1 to 3 orders of magnitude higher than “typical” shelf-depth waters in most other parts of the world, provide the opportunity for enormous sediment transport rates within this coastal mudstream, even under relatively weak currents. The abrupt termination of this inshore band of cold, turbid water as a turbidity front some 25–50 km offshore marks the seaward boundary of the high-transport zone. Landward of the turbidity front, surface waves associated with strong cold-air outbreaks every 7–10 days may destratify the coastal mudstream and entrain additional bottom sediment. Suspended sediments transported into the Korea Strait may accumulate in south-coast embayments, reside in the deep strait, or be carried into the Sea of Japan.

Studying the importance of hurricanes to the northern Gulf of Mexico coast

A pilot study was recently begun dealing with the impacts and post-storm adjustment of barrier islands to severe storms along the northern Gulf of Mexico. The study, funded by the National Science Foundation, may lead to a more comprehensive understanding of coastal morphodynamics and longer term evolution of the coast in that area. Study of the recent impacts and post-storm adjustment of the area to Hurricane Georges is playing a very important role in enhancing our comprehension of the significance of these high-energy events in coastal dynamics. A few hours before dawn on September 28, 1998, Hurricane Georges made landfall near Biloxi along the Mississippi Gulf Coast (Figure 1) as a strong Category 2 system (as defined by the Saffir/Simpson scale: Simpson, 1974). Waves off the Mississippi/Louisiana coast exceeded 10 m in height and storm surge varied between 2–3 m. The entire stretch of coast from the modern Mississippi delta to the Florida Panhandle, a distance in excess of 200 km, was severely impacted by the hurricane through overwash and breaching of the barrier islands, and erosion of the distal ends of the sub-deltas and major distributaries comprising the Birdsfoot delta in Louisiana. Near the landfall zone, the Category 2 storm impacted the coastline with estimated sustained winds of over 45 ms−1, and rainfall between 300 and 400 mm in coastal Mississippi. Georges was the sixth storm to impact this stretch of coast since 1995, the most severe being Hurricane Opal, at its strongest a powerful Category 4 system that made landfall east of Pensacola Beach, Florida, as a marginal Category 3 hurricane [see Eos article by Stone et al., 1996; Lawrence et al., 1998]. The cumulative impact of storms during this period of intense hurricane activity has altered significantly the morphology of the Northwest Florida coast. A review of historical photographs dating back to the early 1900s suggests that the entire coast is now in quite probably the most degraded morphological condition of the 20th century.

Warm‐core eddy discovered in Gulf of Mexico

Thermal infrared satellite data of June 6 and 8 (Figure 1) reveal that a new large warm-core anticyclonic eddy has recently separated from the Loop Current within the Gulf of Mexico. On June 8, the eddys dimensions were 546×300 km, with a center at 26° 20.9′ N latitude, 88° 05.8′W longitude. The eddy was justifiably named “Eddy Whopper.” The distance between the eddy and the Loop Current increased by about 70 km during the 56 hours that elapsed between the images shown. Separation of the eddy was preceded by southwestward advection of cool Florida shelf water observed between May 31 and June 6 (Figure la).

Researchers study impact of Hurricane Opal on Florida coast

On October 4, 1995, over 2000 km of coast-line stretching from southwest Florida to Louisiana was struck by storm-generated waves as Hurricane Opal moved northward across the Gulf of Mexico toward landfall east of Pensacola Beach, Florida (Figure 1). Approximately 12 hours before landfall on October 4, Opal neared category 5 strength (measured on the Saffir/Simpson scale) with sustained wind speeds of over 65 m s−1. Storm surge levels of ∼5 m were estimated across the Northwest Florida shelf by the National Hurricane Center (NHC), resulting in the overwash of most of Santa Rosa Island, the most extensively affected section of coast in the Gulf.

Technical note. Agricultural, hydrologic and oceanographic studies in Bangladesh with NOAA AVHRR data

Abstract This paper presents some results of studies made with NOAA Advanced Very High Resolution Radiometer (AVHRR) data in the fields of agriculture, hydrology and oceanography in Bangladesh. The techniques of processing the raw image data are also discussed. The data for four different dates in 1984 and 1985 have been used. The 1984 data were obtained from NOAA/NESDIS of U.S. A. and the 1985 data were received in real time at the SPARRSO Meteorological Satellite Ground Station. Data from the AVHRR channels 1 and 2 were used to calculate the vegetation index (normalized) which was found to be a useful tool for monitoring vegetation conditions from time to time. These data have also application in monitoring and studying flood conditions in and outside the country. The thermal channels of the AVHRR (channels 4 and 5) have been used for calculating the surface temperatures of the Bay of Bengal. These channels revealed some noteworthy surface features in the Bay.

Satellite observations of the circulation east of the Mississippi delta: cold-air outbreak conditions

Abstract Examination of 12 years of Landsat multispectral scanner images shows a recurrent pattern of westward flow immediately south of the Mississippi-Alabama barrier islands under northerly winds. Such flow patterns are also seen under similar conditions in imagery from the Advanced Very High Resolution Radiometer (AVHRR) of the NOAA-series satellites. The flow enters Chandeleur Sound between Ship Island and the northern end of the Chandeleur Islands. It appears to be driven by northerly winds, which force water south through the ChandeleurBreton Sound, drawing water in from the shelf region south of the Mississippi-Alabama barrier islands. These observations on circulation can be simply explained assuming linear dynamics. These two operational satellite systems are accumulating valuable records of coastal circulation patterns under clear-sky conditions.