ISSN:0143-1161    

DOI:10.1080/014311697217756

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Colour aerial photographs of the Waitemata Harbour, Auckland were scanned at a resolution of 300 dots per inch using a green filter. Ninety in situ water samples were collected at 0.3 m deep during the period when the photographs were being taken, and were used to derive suspended solids concentration (SSC) in a laboratory. The mosaiced photographs were resampled from 1 m to 5 m and 10 m resolutions. The total mass of suspended solids was estimated from the image and the bathymetric data in a GIS. It was found that there is a linear, close relation between SSC and its reflectance on the scanned photographs. The regressed relation has the largest R2 value at 10m. The total mass of suspended solids is estimated at 1401 tons. The main factor affecting the accuracy of estimation is the inconsistency in the tone of the photographs used.

ISSN:0143-1161    

DOI:10.1080/014311697217765

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper describes waveform sampling lidar systems for airborne remote sensing applications. Measurements over complex terrains and open ocean using these lidar systems are described. The lidar detected terrain features during these experiments included forested lands, farm lands, cleared lands, farm roads and lake water. Lidar waveform characteristics as a function of these terrain features are described. Comparisons of lidar waveform over lake water and ocean water are also described.

ISSN:0143-1161    

DOI:10.1080/014311697217774

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper we present first results of bare surface soil moisture retrieval using data from the European Multisensor Airborne Campaign/ Experimental Synthetic Aperture Radar (EMAC/ESAR) collected on 9 April 1994 in the Zwalm catchment, Belgium. Data from EMAC Reflective Optics System Imaging Spectrometer (ROSIS) collected on 12 July 1994 over the same catchment were used to develop land use maps. Concurrent to the EMAC/ESAR overflights field data were collected in two subcatchments of the Zwalm catchment. The paper first presents the data processing procedures used for the radar images. Then we apply a theoretical backscattering model to investigate the sensitivity of EMAC/ESAR backscattering coefficients to surface parameters (topography, surface roughness, vegetation and soil moisture). By comparing the predicted backscattering coefficients to the observed ones, we can conclude that classical measurement techniques for surface roughness parameters in remote sensing campaigns are not accurate enough for retrieving soil moisture using theoretical models. A method based on simultaneous retrieval of surface roughness parameters and soil moisture using multiple ESAR measurements is hence proposed. Promising results for retrieved soil moisture confirm the validity of the proposed method.

ISSN:0143-1161    

DOI:10.1080/014311697217783

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Markov chain canopy reflectance model (MCRM) by Kuusk (1995 b) has been tested versus the ray tracing model on two different computer maquettes of field crops (Barley and Beet), and on the field data collected in the frame of the Franco-English Collaborative Reflectance Experiment in 1989 and 1990 on sugar-beet plots. Separate comparisons of single and multiple scattering components of the MCRM and the ray tracing procedure demonstrated good agreement of the models. Inversion of the MCRM on field data returned good estimates of LAI in the range LAI 0.1-4 using nadir reflectance data in three SPOT and two Landsat TM channels. The estimated chlorophyll content was well correlated to the measured one, although underestimated to some extent. The use of directional data at 45 zenith angle and four azimuth angles improved the estimates of both the LAI and the chlorophyll content. It also permitted the estimation of additional parameters of the canopy structure (leaf size, LAD, the Markov parameter).

ISSN:0143-1161    

DOI:10.1080/014311697217792

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A method of estimation of accumulated precipitation which incorporates numerical model analyses, satellite and surface data has been developed for the African continent. An estimate for accumulated convective cloud precipitation is computed from cold cloud top temperature duration with a bias removal made from the use of rain-gauge data. Orographic precipitation from relatively warm cloud sources is estimated using a combination of surface and satellite data, orography, and numerical model analyses of relative humidity and wind. The results of a comparison of these precipitation estimates with independent rainfall data show this method produces skilful analyses of estimated accumulated precipitation for the Sahel region of Africa.

ISSN:0143-1161    

DOI:10.1080/014311697217800

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Research designed to better define relations between 1-km multitemporal AVHRR-derived NDVI data and selected climatological parameters, soil hydrological properties and land cover characteristics is summarized. Bi-weekly maximum value composite NDVI data and concurrently measured meteorological data acquired in 1990 and 1991 for Nebraska were utilized to study relations between NDVI and accumulated growing degree days,soil temperature, precipitation and potential evapotranspiration. Temporal change in NDVI was found to be closely linked with the temperature regime. NDVI-precipitation and NDVI-potential evapotranspiration relations exhibited time lags, although the length of lag varied with land cover type, precipitation, and soil hydrologic properties. NDVI response to precipitation was stronger in natural grasslands and grassland/wet meadows than in areas of irrigated cropland and mixed crop/ grass. NDVI-climate relations were strongest where vegetation was developed on soils with low root zone available water capacity and high permeability. Relations derived by using NDVI values over 3 pixel by 3 pixel windows showed little difference from those using single 1 km pixel. This may reflect both the relatively homogeneous land cover characteristics of the study area and the effect of off-nadir viewing geometry on AVHRR data acquisition.

ISSN:0143-1161    

DOI:10.1080/014311697217819

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A neural network approach was used to develop acccurate algorithms for inverting a complex forest backscatter model. The model combines a forest growth model with a radar backscatter model. The forest growth model captures natural variations of forest stands (e.g., growth, regeneration, death, multiple species and competition for light). This model was used to produce vegetation structure data typical of transitional/northern boreal hardwood forests in Maine. These data supplied inputs to the radar backscatter model which simulated the polarimetric radar backscatter (C, L, P, X bands) above the forests. Using these simulated data, various neural networks were trained with inputs of different backscatter bands and output parameters of above ground biomass, total number of trees, mean tree height and mean tree age. These trained neural networks act as efficient algorithms for inverting the complex forest backscatter model. The accuracies (r.m.s. and R2 values) for inferring various parameters from radar backscatter were above ground biomass (1.6kg m -2, 0.94), number of trees (48 ha -1, 0.94), tree height (0.47 m, 0.88) and tree age (24.0 years, 0.83). The networks that used only AIRSAR bands (C, L, P) had a high degree of accuracy. The inclusion of the X band with the AIRSAR bands did not seem to increase significantly the accuracy of the networks. The networks that used only the C and L bands still had a relatively high degree of accuracy for all forest parameter (R2 values from 0.75 to 0.91). Modest accuracies (R2 values from 0.65 to 0.84) were obtained with networks that used only the L band and poor accuracies (R2 values from 0.36 to 0.46) were obtained with networks that used only the C band. Several networks were shown to be relatively insensitive to the addition of random noise to radar backscatter. The results demonstrate that complex, forest backscatter models can be efficiently inverted using neural networks that use only radar backscatter data.

ISSN:0143-1161    

DOI:10.1080/014311697217828

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The risk of widespread forest fire has been assessed from information supplied by the AVHRR sensor onboard NOAA satellites, for the area of the Autonomous Community of Valencia in eastern Spain, where several major forest fires occurred in the summer of 1994. The burnt surface data were obtained through unsupervised classification of the spectral information of the forest areas, first, from a date previous to the forest fire; and second, from a date following the fire. The methodology for the forest fire risk evaluation is based on the temporal evolution of the NDVI weekly maximum value. Actual forest fires appear to be statistically correlated with the deduced high risk forest fire areas.

ISSN:0143-1161    

DOI:10.1080/014311697217837

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Optimisation of economic return from forests requires that comprehensive forest inventory data be available to support the design of harvesting strategies. Such inventory data can potentially be obtained by remote sensing. This study investigates the accuracy with which wood volume (m3 ha -1) in a plantation forest can be calculated from Landsat TM data at the pixel and foreststand spatial scales. Wood volumes were estimated from regression analysis, nonparametric line-fitting, and an N-dimensional K-nearest-neighbour classification scheme. At the pixel scale, relations between Landsat data and measured wood volume were found to be significant but weak, with r2 values of 0.3, and with correspondingly poor estimates of wood volume (root-mean-square errors rmses of 100 m3 ha -1). By averaging the pixel-scale estimates, wood volume estimates of acceptable accuracy were obtained for forest-stand areas of about 40 ha (rmses of 46 m3 ha -1). Parametric regression performed slightly better overall than non-parametric line fitting techniques for estimating wood volume. Estimates of similar accuracy to those obtained by regression were also given by NK-classification at the pixel-scale, provided K was large ( 15), although the classifier produced biased results at the forest-stand scale. It is concluded that Landsat TM only provides an acceptable data source for estimating wood volumes in plantation forests for areas of about 40 ha and larger. The very low dynamic range in the Landsat data is probably a significant factor limiting its use for inventory at more detailed scales.

ISSN:0143-1161    

DOI:10.1080/014311697217846

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor