共查询到20条相似文献,搜索用时 31 毫秒
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LAI and chlorophyll estimation for a heterogeneous grassland using hyperspectral measurements 总被引:10,自引:0,他引:10
Roshanak Darvishzadeh Andrew Skidmore Martin Schlerf Clement Atzberger Fabio Corsi Moses Cho 《ISPRS Journal of Photogrammetry and Remote Sensing》2008,63(4):409-426
The study shows that leaf area index (LAI), leaf chlorophyll content (LCC) and canopy chlorophyll content (CCC) can be mapped in a heterogeneous Mediterranean grassland from canopy spectral reflectance measurements. Canopy spectral measurements were made in the field using a GER 3700 spectroradiometer, along with concomitant in situ measurements of LAI and LCC. We tested the utility of univariate techniques involving narrow band vegetation indices and the red edge inflection point, as well as multivariate calibration techniques, including stepwise multiple linear regression and partial least squares regression. Among the various investigated models, CCC was estimated with the highest accuracy (, ). All methods failed to estimate LCC (), while LAI was estimated with intermediate accuracy ( values ranged from 0.49 to 0.69). Compared with narrow band indices and red edge inflection point, stepwise multiple linear regression generally improved the estimation of LAI. The estimations were further improved when partial least squares regression was used. When a subset of wavelengths was analyzed, it was found that partial least squares regression had reduced the error in the retrieved parameters. The results of the study highlight the significance of multivariate techniques, such as partial least squares regression, rather than univariate methods such as vegetation indices in estimating heterogeneous grass canopy characteristics. 相似文献
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C. Wesche S. Riedel D. Steinhage 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(4):381-386
As part of the CryoSat Cal/Val activities and the pre-site survey for an ice core drilling contributing to the International Partnerships in Ice Core Sciences (IPICS), ground-based kinematic GPS measurements were conducted in early 2007 in the hinterland of the German overwintering station Neumayer (8.25 W,70.65 S). The investigated area comprises the regions of the ice ridges Halvfarryggen and Søråsen, which rise from the Ekströmisen to a maximum of about 760 m surface elevation, and have an areal extent of about 100 km×50 km each. Available digital elevation models (DEMs) from radar altimetry and the Antarctic Digital Database show elevation differences of up to hundreds of meters in this region, which necessitated an accurate survey of the conditions on-site. An improved DEM of the Ekströmisen surroundings is derived by a combination of highly accurate ground-based GPS measurements, satellite derived laser altimetry data (ICESat), airborne radar altimetry (ARA), and radio echo sounding (RES). The DEM presented here achieves a vertical accuracy of about 1.3 m and can be used for improved ice dynamic modelling and mass balance studies. 相似文献
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Plant toxic biochemicals play an important role in defense against natural enemies and often are toxic to humans and livestock. Hyperspectral reflectance is an established method for primary chemical detection and could be further used to determine plant toxicity in the field. In order to make a first step for pyrrolizidine alkaloids detection (toxic defense compound against mammals and many insects) we studied how such spectral data can estimate plant defense chemistry under controlled conditions.In a greenhouse, we grew three related plant species that defend against generalist herbivores through pyrrolizidine alkaloids: Jacobaea vulgaris, Jacobaea erucifolia and Senecio inaequidens, and analyzed the relation between spectral measurements and chemical concentrations using multivariate statistics.Nutrient addition enhanced tertiary-amine pyrrolizidine alkaloids contents of J. vulgaris and J. erucifolia and decreased N-oxide contents in S. inaequidens and J. vulgaris. Pyrrolizidine alkaloids could be predicted with a moderate accuracy. Pyrrolizidine alkaloid forms tertiary-amines and epoxides were predicted with 63% and 56% of the variation explained, respectively. The most relevant spectral regions selected for prediction were associated with electron transitions and CH, OH, and NH bonds in the 1530 and 2100 nm regions.Given the relatively low concentration in pyrrolizidine alkaloids concentration (in the order of mg g−1) and resultant predictions, it is promising that pyrrolizidine alkaloids interact with incident light. Further studies should be considered to determine if such a non-destructive method may predict changes in PA concentration in relation to plant natural enemies. Spectroscopy may be used to study plant defenses in intact plant tissues, and may provide managers of toxic plants, food industry and multitrophic-interaction researchers with faster and larger monitoring possibilities. 相似文献
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Peter Gege Jochen Fries Peter Haschberger Paul Schtz Horst Schwarzer Peter Strobl Birgit Suhr Gerd Ulbrich Willem Jan Vreeling 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(4):387-397
A new facility designed to perform calibration measurements of airborne imaging spectrometers was established at the German Aerospace Center (DLR) in Oberpfaffenhofen. This Calibration Home Base (CHB) is optimized to characterize radiometrically, spectrally, and geometrically the APEX (Airborne Prism Experiment) imaging spectrometer, which is currently being developed under the authority of the European Space Agency (ESA). It however can be used for other optical sensors as well. Computer control of major laboratory equipment allows automation of time consuming measurements. In APEX configuration (wavelength range: 380 to 2500 nm, instantaneous field of view: 0.48 mrad, field of view: ±14) spectral measurements can be performed to a wavelength uncertainty of ±0.15 nm, geometric measurements at increments of 0.0017 mrad across track and 0.0076 mrad along track, and radiometric measurements to an uncertainty of ±3% relative to national standard. The CHB can be adapted to similar sensors (including those with thermal infrared detectors) by exchanging the monochromator’s lamp, the gratings and the filters, and by adjusting the distance between the sensor and folding mirror. 相似文献
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O. Remmer 《Journal of Geodesy》1971,45(1):29-36
As it has been shown by Kubik it is possible to get an estimate,
, of the reciprocal of the weight-matrix in an adjustment problem. If we want to see whether this new estimate
differssignificantly from our a priori valueQ
0 it is necessary to know the distribution function of the elements
, the
’s being the elements of
. This distribution is found in the present article and it is shown that it is not identical with any of the distributions
well known from statistical textbooks. Furthermore a way of computing this new distribution is presented. Finally the connection
with the chi-square distribution is explored and it is proved that the chi-square-distribution may be used as an approximation
for a large number of over-determinations. 相似文献
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Show me the code: spatial analysis and open source 总被引:3,自引:1,他引:2
Sergio J. Rey 《Journal of Geographical Systems》2009,11(2):191-207
This paper considers the intersection of academic spatial analysis with the open source revolution. Its basic premise is that
the potential for cross-fertilization between the two is rich, yet some misperceptions about these two communities pose challenges
to realizing these opportunities. The paper provides a primer on the open source movement for academicians with an eye towards
correcting these misperceptions. It identifies a number of ways in which increased adoption of open source practices in spatial
analysis can enhance the development of the next generation of tools and the wider practice of scientific research and education.
相似文献
Sergio J. ReyEmail: |
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