Water-removed spectra increase the retrieval accuracy when estimating savanna grass nitrogen and phosphorus concentrations   总被引：2，自引：0，他引：2  

Abel Ramoelo  Andrew K. SkidmoreMartin Schlerf  Renaud MathieuIgnas M.A. Heitkönig 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(4):408-417

Information about the distribution of grass foliar nitrogen (N) and phosphorus (P) is important for understanding rangeland vitality and for facilitating the effective management of wildlife and livestock. Water absorption effects in the near-infrared (NIR) and shortwave-infrared (SWIR) regions pose a challenge for nutrient estimation using remote sensing. The aim of this study was to test the utility of water-removed (WR) spectra in combination with partial least-squares regression (PLSR) and stepwise multiple linear regression (SMLR) to estimate foliar N and P, compared to spectral transformation techniques such as first derivative, continuum removal and log-transformed (Log(1/R)) spectra. The study was based on a greenhouse experiment with a savanna grass species (Digitaria eriantha). Spectral measurements were made using a spectrometer. The D. eriantha was cut, dried and chemically analyzed for foliar N and P concentrations. WR spectra were determined by calculating the residual from the modelled leaf water spectra using a nonlinear spectral matching technique and observed leaf spectra. Results indicated that the WR spectra yielded a higher N retrieval accuracy than a traditional first derivative transformation (R²=0.84, RMSE = 0.28) compared to R²=0.59, RMSE = 0.45 for PLSR. Similar trends were observed for SMLR. The highest P retrieval accuracy was derived from WR spectra using SMLR (R²=0.64, RMSE = 0.067), while the traditional first derivative and continuum removal resulted in lower accuracy. Only when using PLSR did the first derivative result in a higher P retrieval accuracy (R²=0.47, RMSE = 0.07) than the WR spectra (R²=0.43, RMSE = 0.070). It was concluded that the water removal technique is a promising technique to minimize the perturbing effect of foliar water content when estimating grass nutrient concentrations.  相似文献   

Response of juvenile lemon sharks, Negaprion brevirostris, to a magnetic barrier simulating a beach net     

Craig P. O’Connell  Daniel C. Abel  Samuel H. Gruber 《Ocean & Coastal Management》2011,54(3):225-230

Beach nets are preventative devices used to minimize interactions between potentially harmful sharks and unsuspecting swimmers. Quantitative studies demonstrated that beach nets drastically reduced local elasmobranch populations, as well as caused considerable bycatch mortality. For this experiment, a beach net-like device was constructed and the behaviors of six juvenile lemon sharks (Negaprion brevirostris) were analyzed. Induced by olfactory and gustatory cues, sharks were given the choice to swim through a magnetic or control opening in the net. In the first trial, all six sharks avoided the magnetic region and significantly preferred to swim through the control region of the fence. The magnetic stimulus no longer affected the swimming behavior of three sharks retested after resting 24 h. Results from the retested sharks were correlated with those from repeated tonic immobility trials, which demonstrated a linear decrease in sensitivity to repeated magnetic stimulation. This study serves as a baseline experiment demonstrating that permanent magnets may substantially decrease elasmobranch mortality within beach nets.  相似文献   

The spherical interpolation method of source localization   总被引：1，自引：0，他引：1  

Smith  J. Abel  J. 《Oceanic Engineering, IEEE Journal of》1987,12(1):246-252

A closed-form least squares approximate maximum likelihood method for localization of broad-band emitters from time-difference-of-arrival (TDOA) measurements, called the spherical interpolation (SI) method, is presented. The localization formula is derived from least squares "equation-error" minimization. Computer simulation results show that the SI method has variance approaching the Cramer-Rap lower bound.  相似文献   

Einfluß der Luftmassen auf den Jahresgang der Poliomyelitis in Mitteleuropa     

Dr. H. Abel  Prof. Dr. A. Baumgartner  Dr. W. Donle 《Theoretical and Applied Climatology》1974,22(1-2):169-196

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Taking issue with PPARC over STP     

Gary Abel  James Wild  Mick Denton 《Astronomy& Geophysics》2007,48(1):1.08-1.09

Following the PPARC programmatic review announced in the spring of last year, with its gloomy outlook for solar–terrestrial physics, three young scientists in the field mobilized the junior members of the STP community. Gary Abel, Jim Wild and Mick Denton tell the story which led to an unprecedented meeting of early-career scientists, followed by an informative meeting with PPARC chief executive Prof. Keith Mason.  相似文献   

Assessment of the reliability of 2D inversion of apparent resistivity data     

Abel I. Olayinka  Ugur Yaramanci 《Geophysical Prospecting》2000,48(2):293-316

The reliability of inversion of apparent resistivity pseudosection data to determine accurately the true resistivity distribution over 2D structures has been investigated, using a common inversion scheme based on a smoothness‐constrained non‐linear least‐squares optimization, for the Wenner array. This involved calculation of synthetic apparent resistivity pseudosection data, which were then inverted and the model estimated from the inversion was compared with the original 2D model. The models examined include (i) horizontal layering, (ii) a vertical fault, (iii) a low‐resistivity fill within a high‐resistivity basement, and (iv) an upfaulted basement block beneath a conductive overburden. Over vertical structures, the resistivity models obtained from inversion are usually much sharper than the measured data. However, the inverted resistivities can be smaller than the lowest, or greater than the highest, true model resistivity. The substantial reduction generally recorded in the data misfit during the least‐squares inversion of 2D apparent resistivity data is not always accompanied by any noticeable reduction in the model misfit. Conversely, the model misfit may, for all practical purposes, remain invariant for successive iterations. It can also increase with the iteration number, especially where the resistivity contrast at the bedrock interface exceeds a factor of about 10; in such instances, the optimum model estimated from inversion is attained at a very low iteration number. The largest model misfit is encountered in the zone adjacent to a contact where there is a large change in the resistivity contrast. It is concluded that smooth inversion can provide only an approximate guide to the true geometry and true formation resistivity.  相似文献   

The environmental setting of the harbor of the classical site of Oeniades on the Acheloos delta,Greece     

ric Fouache  Rmi Dalongeville  Stphane Kunesch  Jean‐Pierre Suc  Danica Subally  Abel Prieur  Pierre Lozouet 《Geoarchaeology》2005,20(3):285-302

Using a multidisciplinary approach, the Holocene geomorphological and palaeoenvironmental dynamics of the Acheloos delta were studied in order to understand how the ancient port of Oeniades, today situated 5 km from the sea, was connected to the sea in ancient times. A study of ancient maps, aerial photographs, and a SPOT image enabled us to reconstitute the successive changes in the flow of the Acheloos River and to conclude that, contrary to the traditional thesis of historians and archeologists, the harbor of Oeniades was completely independent from the river during Antiquity. Multidisciplinary studies (sedimentology, malacology, palynol‐ogy, and radiocarbon dating) were carried out on sediments from two boreholes (OEN1 and OEN2). Results show that the port of Oeniades communicated directly with an open bay that was created at the peak of the last post‐glacial transgression. The bay was gradually filled with sediments, allowing human occupation of the area to progress. © 2005 Wiley Periodicals, Inc.  相似文献   

Evolution of Stratocumulus Over Land: Comparison of Ground and Aircraft Observations with Numerical Weather Prediction Simulations     

Simon R. Osborne  Steven J. Abel  Ian A. Boutle  Franco Marenco 《Boundary-Layer Meteorology》2014,153(2):165-193

Forecasting of low cloud continues to challenge numerical weather prediction. With this in mind, surface and airborne observations were made over East Anglia, UK, during March 2011 to investigate stratus and stratocumulus advecting from the sea over land. Four surface sites were deployed at various distances inland aligned approximately along the flow. In situ data include cloud-droplet measurements from an aircraft operating off the coast and a tethered balloon 100 km inland. Comparisons of thermodynamic and cloud properties are made with Met Office operational model simulations at horizontal resolutions of 4 and 1.5 km. The clouds contained droplet concentrations up to 600 cm \(^{-3}\) within polluted outflow off Europe. These measurements were compared to three different model schemes for predicting droplet concentration: two of them perform well at low to moderate concentrations but asymptote to 375 cm \(^{-3}\) . Microwave radiometers at the ground sites retrieved liquid water paths that reduced with distance inland and were generally below 200 g m \(^{-2}\) . The modelled water path performs well upstream but more erratically far inland. Comparisons of thermodynamic profiles are made within both Lagrangian and Eulerian frameworks and show the model predicted changes in equivalent potential temperature generally within 1 K, with occasional errors of 2 K or more. The modelled cloud-top temperatures were in good agreement with the observations down to \(-\) 7  \(^{\circ }\) C, but the magnitude of the temperature inversion, although good at times, was too small by on average 1.6 K. The different simulations produced different cloud-top water contents due to a combination of resolution and scientific upgrades to the model, but they generally underestimate the amount of cloud water. Major changes, such as the mesoscale temporary cloud breaks on 2 March 2011 and the complete clearance on 4 March, were seemingly predicted by the model for the correct reasons.  相似文献