Temporal dynamics of soil and vegetation spectral responses in a semi-arid environment

This paper discusses several difficulties encountered in detecting and monitoring temporal changes in vegetation using multispectral imagery from airborne or spaceborne sensors. These difficulties are due to (1) temporal change in the vegetation state; (2) temporal change in the soil/rock signature; and (3) difficulty in discriminating vegetation from soil or rock background. The seasonal dynamics of soil and vegetation was investigated over two years on permanent sample plots in a natural fenced-off area in the semi-arid region (200 mm annual average rainfall) of the Northern Negev, Israel. Results show that temporal analysis of natural vegetation in semi-arid regions should take into account three ground features--perennials, annuals, and biological soil crusts; all having phenological cycles with the same basic elements--oscillation from null (or low) to full photosynthetic status. However, these cycles occur in successive periods throughout the year. The phenological cycle of perennial plants is related to the adaptation of desert plants to scarcity of water. Annuals are green only for a relatively short period during the wet season and turn into dry organic matter during the summer. The microphytic communities (lower plants) of the biological soil crusts are rapidly affected by moisture and turn green immediately after the first rain, in a timescale of minutes. In arid environments, where the higher plants are sparse, this type of plant has considerable importance in the overall production of the greenness signal. However, crust-covered areas are visually similar to bare soil throughout the dry period. This paper concludes that a priori knowledge of the phenological changes in desert plants (lower and higher) is valuable in the interpretation of remote sensing data of arid environments. It is shown that rainfall amount and regime are the keys for understanding the dynamic processes of the different ground features. Through polynomial fitting, simple functions describing the annual variations in the NDVI of the different cover types have been formulated and validated; showing the feasibility and viability of modelling the processes. Although fluctuations in the rainfall regime between years poses a problem to designing a unique model, it is believed that such a problem can be overcome with long-term observations.     

Predisposition to the fragile X syndrome in Jews of Tunisian descent is due to the absence of AGG interruptions on a rare Mediterranean haplotype

Lesbians may engage in behavior that places their health at risk and may delay health care and screening more than do their heterosexual counterparts. This article examines influences on lesbians' health risk factors and health-seeking behaviors. A statewide, self-administered survey of members of a lesbian community organization was performed. Univariate and bivariate analyses were calculated, and linear regression was used to examine models of health risks and health-seeking behavior. Of 324 respondents, 90% had disclosed sexual orientation to at least one provider, 22% reported seeking care without symptoms (preventive care), and 23% reported waiting until symptoms are at their worst or never seeking care. Young age, belief in the importance of lung cancer, difficulty of getting health care when needed, reliance on the partner for health support, and fewer male partners were all associated with greater health risk for lesbians. Difficulty obtaining health care, difficulty communicating with the primary care provider, discomfort in discussing depression, and degree of comfort in discussing menopause were all associated with a delay in seeking health care. Sensitive communication with lesbians and further identification of lesbians' specific barriers to care may improve health-seeking behavior and provide more opportunities for screening and risk factor counseling in this population.     

Radiometric and photometric determinations of simulated shallow-water environment

Optical remote sensing is increasingly becoming a preferred economic alternative to the traditional in situ observations and physical sampling for mapping and monitoring habitats. Submersed habitats, such as eelgrass and corals, are especially challenging for field work. Even for remote-sensing work, a priori knowledge of environmental factors is required for highly accurate analysis. Background illumination and water clarity are two key factors that affect the optical remote-sensing imagery, which may vary widely with season, time of year, geographic location, or water depth. This article presents efforts to simulate natural oceanic conditions in a laboratory setting. Solar radiation predicted at different latitudes under varying water clarity conditions and depth were replicated using a 2.5 m deep wave tank at the University of New Hampshire. The goals of the study were: (1) to simulate illumination and water clarity conditions that approximate coastal and oceanic waters, and (2) to quantify the impact of the simulated illumination and water clarity conditions at different depths on the apparent colours that can be observed from an aerial platform. The empirical radiometric measurements included irradiance, radiance, and remote-sensing reflectance from an underwater array of light sources. The results of the study show good correlation (r ²?=?0.89–0.93) between the natural daylight spectrum at the water surface and the irradiance measurements between 350 nm and 590 nm, at 3.5 m from the light array. The colours of the clear and murky water types were photometrically calculated from the radiometric measurements and validated using underwater video imagery. Using this methodology, illumination and water clarity can be replicated under controlled laboratory conditions and used to assist in studying the physical, chemical, and biological processes in habitats, at varied geographic locations and differing environments.     

Field calibration and validation of remote-sensing surveys

The Optical Collection Suite (OCS) is a ground-truth sampling system designed to perform in situ measurements that help calibrate and validate optical remote-sensing and swath-sonar surveys for mapping and monitoring coastal ecosystems and ocean planning. The OCS system enables researchers to collect underwater imagery with real-time feedback, measure the spectral response, and quantify the water clarity with simple and relatively inexpensive instruments that can be hand-deployed from a small vessel. This article reviews the design and performance of the system, based on operational and logistical considerations, as well as the data requirements to support a number of coastal science and management projects. The OCS system has been operational since 2009 and has been used in several ground-truth missions that overlapped with airborne lidar bathymetry (ALB), hyperspectral imagery (HSI), and swath-sonar bathymetric surveys in the Gulf of Maine, southwest Alaska, and the US Virgin Islands (USVI). Research projects that have used the system include a comparison of backscatter intensity derived from acoustic (multibeam/interferometric sonars) versus active optical (ALB) sensors, ALB bottom detection, and seafloor characterization using HSI and ALB.