| 1. |
- Eklundh, L.
(författare)
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Tillförlitlig global vegetationsinformation fran satellitdata-optimism eller realitet?
- 1997
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Ingår i: Svensk Geografisk Arsbok. - 0081-9808. ; 73, s. 7-15
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Tidskriftsartikel (refereegranskat)abstract
- The continuous operation of the NOAA series of meteorological satellites from the early 1980s onward, and the use of time series of data from its AVHRR sensor have been instrumental in the development of a new paradigm in the area of global earth observation. The coarse spatial and high temporal resolution of the data contrasts sharply with the data characteristics of traditional earth resource satellites, such as Landsat and SPOT, with their high spatial and low temporal resolution. Numerous scientists have demonstrated the potential of the data for capturing seasonal variations in terrestrial vegetation. The enthusiam of researchers has led them to use time series of ANHRR data for almost every conceivable type of study, from mapping of deserts and forests to the monitoring of ecological conditions for locust infestations and the spread of malaria by mosquitoes, AVHRR data are not being used operationally in programmes issuing early warnings for drought and famine in semi-arid areas. However, studies of the quality of the data cast some doubts over previous optimism. How do we come to terms with the contradictory results and what are the implications for the future use of the data?.
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| 2. |
- Zhou, Q., et al.
(författare)
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On the ground estimation of vegetation cover in Australian rangelands
- 1998
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 19:9, s. 1815-1820
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Tidskriftsartikel (refereegranskat)abstract
- A number of field techniques were assessed on their reliability for estimating vegetation cover in Australian rangelands. The field sampling was undertaken using visual estimation, line intercepts, a crown cover model, and images acquired from a digital camera. The results from these methods were compared and analysed. The data obtained from these differing methods agree with each other in relative rather than absolute terms. This suggests that the methods can provide a reasonable basis for qualitative remote sensing studies, but are not suitable for quantitative investigations.
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| 3. |
- Ban, Yifang, et al.
(författare)
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Multitemporal ERS-1 SAR data for crop classification: a sequential-masking approach
- 1999
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Ingår i: Canadian journal of remote sensing. - : Informa UK Limited. - 0703-8992 .- 1712-7971. ; 1999:25, s. 438-447
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Tidskriftsartikel (refereegranskat)abstract
- Based on photo-interpretation procedures, the technique of sequential masking can be used to differentiate image features using a series of multitemporal images. In this study, a set of nine ERS-1 SAR images is analyzed using this technique to determine the earliest dates for identifying different crop types in an agricultural area of southern Ontario, Canada. SAR temporal backscatter profiles of crops were generated from calibrated radar imagery. Based on these temporal backscatter profiles, per-field classifications using the sequential-masking technique were performed on the early- and mid-season multitemporal SAR data. It was found that using only three images, acquired on May 31, June 16 and July 5, it is possible to differentiate winter wheat, alfalfa/hay, barley/oats, soybeans and corn with an overall validation accuracy of 88.5% and a Kappa coefficient of 0.85.
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| 4. |
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| 5. |
- Ban, Yifang, et al.
(författare)
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Orbital effects on ERS-1 SAR temporal backscatter profiles of agricultural crops
- 1998
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 19:17, s. 3465-3470
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Tidskriftsartikel (refereegranskat)abstract
- Multi-temporal radar backscatter characteristics of crops and their underlying soils were analysed for an agricultural area in south-western Ontario, Canada using nine dates of ERS-1 SAR imagery acquired during the 1993 growing season. From the calibrated data, SAR temporal backscatter profiles were generated for each crop type. The results indicate that small changes in incidence-angle can have strong impacts on radar backscatter. Thus, attention must be given to local incidence-angle effects when using ERS-1 SAR data,especially when comparing backscatter coefficients of the same area from different scenes or different areas within the same scene.
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| 6. |
- Seaquist, Jonathan, et al.
(författare)
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A simple method to account for off-nadir scattering in the NOAA/NASA Pathfinder AVHRR Land Data Set
- 1998
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Ingår i: International Joural of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 19:7, s. 1425-1431
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Tidskriftsartikel (refereegranskat)abstract
- The radiometric distortion of reflected radiation received by the NOAA AVHRR sensor is brought on by the effects of viewing and solar illumination geometry, as well as atmospheric effects. This may lead to a gross underestimation of bioproductivity or crop yield from models which use high temporal resolution NOAA AVHRR data as an input. Accordingly, a simple angular correction method is presented using daily NDVI data over the Sudan from July, 1989 derived from the NOAA/NASA Pathfinder AVHRR Land Data Set. Its simplicity and expediency may render it suitable for operational monitoring programmes such as famine early warning.
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