Atmospheric Corrections Using MODTRAN for TOA and Surface BRDF Characteristics from High Resolution Spectroradiometric/Angular Measurements from a Helicopter Platform

High-resolution spectral radiance measurements were taken by a spectral radiometer on board a heli copter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution. The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to re trieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region. Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattering contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance dif ference and ratio that many remote sensing techniques are based on, such as the normalized difference vege tation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the veg etation type and solar zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth＇s Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25° solar zenith angle and 0.15 at 50° solar zenith angle, respectively.     

Near-surface Microearthquakes at The Geysers Geothermal Field, California

—?A 150-m length, 6-level, three-component, vertical geophone array was cemented into the 67- to 219-m depth interval (220 to 720?ft) of Unocal's well GDCF 63-29 during a plug and abandonment operation on April 7, 1998. Casing deformation has been observed in wells of the study area including the GDCF 63-29 well. An objective of the study was to determine if shallow deformation at The Geysers is manifested seismically. Near-surface microearthquake activity was monitored for a period of one year; during the latter four months, monitoring was supplemented with four surface stations to help constrain locations of shallow seismicity. Event locations occurring within about 750?m of the array bottom have been determined for the 10-week period January 6 to March 16, 1999. These events are distinct from surface-monitored seismicity at The Geysers in that they occur predominantly above the producing reservoir, at depths ranging from about 220 to 1000?m (600 to ?180?m elevation). The shallow events tend to be episodic, with relatively quiescent periods of up to three weeks occurring between swarms. Event locations show a northeast-striking trend, similar to seismicity trends mapped deeper in the reservoir, and parallel to the strike of a major surface lineaments observed over the productive field. However, clear fault or fracture planes are not resolved from the hypocenters. Composite fault-plane solutions suggest oblique reverse faulting in the overburden. The shallowest seismicity terminates near the base of a serpentine unit, a contact which is the locus of most of the well casing deformations logged in the area, suggesting that reservoir contraction is accommodated along numerous discrete faults below the serpentine, but as continuous plastic deformation in the serpentine. It is hypothesized that the resulting strain discontinuity at the base of the serpentine explains the prevalence of wellbore deformation there. The shallow, above-reservoir microseismicity is strongly correlated in time with the injection and the deeper injection-induced seismic activity occurring in the reservoir immediately below. This suggests that deep injection-induced events trigger shallower events, by a remote triggering mechanism which has been observed at a larger scale at The Geysers and elsewhere.     

Fish Utilization of Created vs. Natural Oyster Reefs (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>)

Once viewed as an inexhaustible fishery resource, eastern oyster reefs (Crassostrea virginica) have been dramatically depleted. In North Carolina alone, eastern oyster harvests have declined by 90% since the early 1900s. However, eastern oyster restoration and management efforts have substantially increased since the 1970s. Oyster reefs provide habitat and refuge for organisms, improve water quality, and decrease erosion. Oyster restoration projects aim to construct reefs that function similarly to their natural counterparts. Therefore, post-creation monitoring of these reefs is crucial in determining restoration success. However, monitoring is often lacking or focused only on oyster density and size rather than ecosystem functions such as nekton utilization. This study examines nekton utilization among created reefs compared to natural reefs in an estuary in Wilmington, North Carolina. The objective was to determine whether the created reefs function similarly to the natural reefs in abundance, species richness, and fish size. Using seine nets and Breder traps, reefs were sampled over a 5-month period. No significant difference was detected among reefs for nekton abundance, species richness, and standard length. This is a promising result for future management, indicating that created and natural reefs can support similar communities of fishes and shrimp.     

Use of the analytical modeling of recession to describe a dual-aquifer effect

Hydrogeology Journal - Complex recession properties can be described using a fairly simple analytical model. The model used in this study is PULSE, which is used to estimate groundwater recharge...     

Abundance and seasonality of meiofauna,including harpacticoid copepod species,associated with stems of the salt-marsh cord grass,Spartina alterniflora

Ten Spartina alterniflora plants were sampled monthly in a Louisiana estuary to determine the abundance and species composition of stem-dwelling meiofauna and small macrofauna. Most organisms were associated with epiphytic algae found relatively high on standing stems; one harpacticoid copepod, Leptocaris brevicornis, was associated with vascular tissue. Only 15% of the stem fauna was found within 6 cm of the sediment surface. Highest abundance of total meiofauna (>8,000 individuals per 100 cm² stem surface) occurred in July. The overall seasonal average was 1,563 individuals per 100 cm² (about 800 per stem). Nematodes (24% of the total) and harpacticoids (adults and copepodites 19%, and nauplii 15%), were abundant and omnipresent taxa. Rotifers (30%) were limited to the summer months, but were extremely abundant when present, 5,037 individuals per 100 cm² in July. Mites were common (10%) while several groups, for example, amphipods, isopods, polychaetes, and insect larvae, were rare. The stem harpacticoid assemblage was not diverse; four sediment-dwelling and three species reported only from stems were recorded. Overall, abundance was low from December to May, and high from June through November. Winter and spring minima may have resulted from several factors. Estuarine water levels in the Gulf of Mexico are lowered by as much as 25 cm in the winter, and stems likely were desiccated. Highest rhizomatic growth occurs in the spring, and the resulting reduced epiphyte populations may have influenced meiofauna. The density of stem meiofauna above the sediment surface averaged about 225 individuals per 10 cm² sediment surface, but frequently exceeded that in the surrounding sediments.     

The evolution of Rapid Burster outbursts

We describe the evolutionary progression of an outburst of the Rapid Burster. Four outbursts have been observed with the Rossi X-Ray Timing Explorer between 1996 February and 1998 May, and our observations are consistent with a standard evolution over the course of each. An outburst can be divided into two distinct phases. Phase I is dominated by type I bursts, with a strong persistent emission component; it lasts for 15–20 d. Phase II is characterized by type II bursts, which occur in a variety of patterns. The light curves of time-averaged luminosity for the outbursts show some evidence for reflares, similar to those seen in soft X-ray transients. The average recurrence time for Rapid Burster outbursts during this period was 218 d, in contrast to an average ∼180‐d recurrence period observed during 1976–1983.     

Loess stratigraphy of the Lower Mississippi Valley

Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses.

Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses.