Donald C. Rundquist

Relationship between gross primary production and chlorophyll content in crops: Implications for the synoptic monitoring of vegetation productivity

CO2/m 2 s in maize (GPP ranged from 0 to 3.1 mg CO2/m 2 s) and less than 0.2 mg CO2/m 2 s in soybean (GPP ranged from 0 to 1.8 mg CO2/m 2 s). Validation using an independent data set for irrigated and rainfed maize showed robustness of the technique; RMSE of GPP prediction was less than 0.27 mg CO2/m 2 s.

Comparison of NIR/RED ratio and first derivative of reflectance in estimating algal-chlorophyll concentration: A case study in a turbid reservoir

Abstract The objective of this research was to test the use of the well-documented ratio of near-infrared (NIR; 705 nm) to red (670 nm) reflectance in estimating chlorophyll content in a relatively turbid midwestern reservoir. The results were compared with those obtained by analyzing the first derivative of reflectivity near 690 nm. Data were collected in three different months over a 2-year period, and the characteristic spectral features of surface reflectance associated with algal chlorophyll were analyzed. Results indicated that the NIR/red ratio was not an effective predictor of algal-chlorophyll concentration in our case, except on one occasion. The first derivative of reflectance, on the other hand, was better correlated with chlorophyll concentration than the 705/670 band ratio. The highest correlation between the first derivative and chlorophyll was at 690.7 nm.

Benthic Habitat Mapping in Tropical Marine Environments Using QuickBird Multispectral Data

The objective of this research focused on the utility of QuickBird multispectral data for identifying and classifying tropical-marine benthic habitats after applying atmospheric and water-column corrections for an area around Roatan Island, Honduras. Atmospheric (Rayleigh and aerosol path radiance) and water column corrections (water depth and water column attenuation) were applied to the imagery, making it an effective method for mapping benthic habitats. Water depth for each pixel was calculated based on a linear model by regressing transformed radiance over known homogenous benthos against measured depths. Water column correction was achieved by deriving absorption and backscattering coefficients for each band of the image using a 50 � 50 window of clear water pixels. Corrections for water path radiance and water column attenuation of the bottom reflected radiance were made for the entire scene, allowing the bottom albedo to be determined for shallow coastal areas. An image of the bottom (i.e., an albedo image), minus the water column, was produced. Albedos were ≤8 percent for seagrass benthos, approximately 8 to 18 percent for coral areas, and ≥18 percent for sand dominated areas. An unsupervised classification algorithm was applied to the bottom albedo image, generating a classified map of benthic habitats. Accuracy assessment based on 383 reference points revealed an overall accuracy of 81 percent, with an overall Kappa value of 0.774.

Remote estimation of nitrogen and chlorophyll contents in maize at leaf and canopy levels

a b s t r a c t Leaf and canopy nitrogen (N) status relates strongly to leaf and canopy chlorophyll (Chl) content. Remote sensing is a tool that has the potential to assess N content at leaf, plant, field, regional and global scales. In this study, remote sensing techniques were applied to estimate N and Chl contents of irrigated maize (Zea mays L.) fertilized at five N rates. Leaf N and Chl contents were determined using the red-edge chlorophyll index with R2 of 0.74 and 0.94, respectively. Results showed that at the canopy level, Chl and N contents can be accurately retrieved using green and red-edge Chl indices using near infrared (780-800 nm) and either green (540-560 nm) or red-edge (730-750 nm) spectral bands. Spectral bands that were found optimal for Chl and N estimations coincide well with the red-edge band of the MSI sensor onboard the near future Sentinel-2 satellite. The coefficient of determination for the relationships between the red-edge chlorophyll index, simulated in Sentinel-2 bands, and Chl and N content was 0.90 and 0.87, respectively.

The spectral responses of algal chlorophyll in water with varying levels of suspended sediment

Abstract The purpose of this paper is to investigate the spectral responses of algal chlorophyll and water, under natural sunlight with varying suspended sediment concentrations (SSC). Twenty levels of SSC with each of two sediment types were generated, ranging from 50 to 1000 mgl−1, in 75101 of water containing chlorophyll-a concentrations of 718 μgl−1 and 295 μgl−1. Results indicate that suspended sediments do not eliminate the prominent spectral patterns of algal chlorophyll, even as SSC reached 1000 mgl−1. Between 400 and 900 nm, the relation between reflectance and SSC satisfies the expression: d2R(λ)/dS2<0. The effects of varying SSC on the positions and magnitudes of pronounced chlorophyll features were investigated. The ratio between the NIR and red wavelengths was totally independent of SSC. Thus, our finding supports using it as an index for measuring chlorophyll in natural surface water containing suspended sediments.

Satellite Change Detection Analysis of Deforestation Rates and Patterns along the Colombia – Ecuador Border

Abstract This study uses Landsat satellite data to document the rates and patterns of land-cover change along a portion of the Colombia-Ecuador border during a 23-yr period (1973–1996). Human colonization has resulted in extensive deforestation in both countries. Satellite change detection analysis showed that the annual rates of deforestation were considerably higher for the Colombian side of the border. In addition, loss of forest cover on the Colombian side for the study period was almost 43%, while only 22% on the Ecuadorian side. The study found that there is no single factor driving deforestation on either side of the border, but concluded that the higher rates on the Colombian side may be due to higher colonization pressures and intensification of illegal coca cultivation. On the Ecuador side of the border the satellite images documented patterns of deforestation that reflected road networks associated with oil exploration and development.

A review of wetlands remote sensing and defining new considerations

Significant progress has been made in using remote sensing as a means of acquiring information about wetlands. This research provides a brief review of selected previous works, which address the issues of wetland identification, classification, biomass measurement, and change detection. Suggested new research emphases include compiling basic spectral‐reflectance characteristics for individual wetland species by means of close‐range instrumentation, analyzing canopies architectures to facilitate species identification, and assessing the impact on composite spectral signatures of wet soils and variable depths of standing water beneath emergent canopies. These research foci are justifiable when considered in the context of environmental change / variability and the production of trace gases.

Statewide groundwater‐vulnerability assessment in nebraska using the drastic/GIS model

Abstract The paper summarizes a technique for implementing the “DRASTIC” groundwater‐vulnerability model within the context of an automated raster‐based geographic information system. Discussion focuses on a methodological development and a statewide project completed recently in Nebraska. The final products, a comprehensive flow chart illustrating procedures and a map of calculated potential pollution hazard, are presented. The methodology can be executed successfully with minimal training and experience. Areas of Nebraska considered vulnerable to groundwater pollution are identified.

Comparative reflectance properties of algal cultures with manipulated densities

A comparative study was conducted with representatives of four ecologically important freshwater algal phyla (Chlorophyta, Cyanophyta, Bacillariophyta and Pyrrophyta) in order to (1) analyze the relationship between reflectance spectral features and algal density, and (2) to elucidate and characterize possible diagnostic spectral reflectance features for identification of dominant groups in algal bloom states. Algae (two chlorophytes, a cyanophyte and a bacillariophyte) were cultured in mesocosm tanks and then their densities were reduced through dilution with clear water in four experiments. In a fifth experiment, use was made of the pyrrophyte Peridinium gatunense, which bloomed in Lake Kinneret, Israel, practically forming a unialgal ‘culture’. The basic quantitative procedures for spectroradiometeric measurements and support data collection (pigment concentrations) were consistent among the experiments. Several spectral reflectance characteristics were found to be common to all the species examined in the study: a depression between 440 and 500 nm, a salient trough around 670 nm, and prominent peaks centered around 570 nm and 700 nm. The increase in magnitude of a near infra-red peak and shift of its position towards longer wavelengths with increased chlorophyll- a concentration was found to be a common trait for all the species studied. Other specific spectral reflectance features were also found and are discussed here. Quantitatively different relationships of magnitude and position of spectral reflectance features with chlorophyll- a concentration reflect different optical properties of algae (their scattering and absorption). This may be useful for taxonomic characterization by remote sensing.

High-resolution ocean color remote sensing of benthic habitats: a case study at the Roatan island, Honduras

Natural resource managers clamor for detailed reef habitat maps for monitoring smaller scale disturbances in reef communities. Coastal ocean color remote sensing techniques permit benthic habitats to be explored with higher resolution than ever before. The objective of this research was to develop an accurate benthic habitat map for an area off the northwest coast of Roatan Island, Honduras, using high-resolution multispectral IKONOS data. Atmospheric (Rayleigh and aerosol path radiance) and water column corrections (water depth and water column attenuation) were applied to the imagery, making it a robust method for mapping benthic habitats. Water depth for each pixel was calculated based on a site-specific polynomial model. A mechanistic radiative transfer approach was developed that removed the confound effect of the water column (absorption and scattering) from the imagery to retrieve an estimate of the bottom reflectance (albedo). Albedos were /spl les/ 12% for seagrass benthos, 12% to 24% for coral areas, and /spl ges/ 24% for sand-dominated areas. The retrieved bottom albedos were then used to classify the benthos, generating a detailed map of benthic habitats, followed by accuracy assessment.