Geography Reference
In-Depth Information
important to understand the rapid seasonal changes of the crops or other Earth
surface features of interest (mainly natural vegetation). To this end, crop calendars
can be developed for any particular geographic area. Crop calendars describe the
general characteristics of the different crops types as a function of the time of year
and the geographic location. They can vary from one year to the next, depending
on the various conditions such as extreme weather events of that particular year.
Finally, crop calendars should be developed more well in areas of the world where
seasonal changes are distinct'' (Hoffer 1980 ).
Crop phenology (regular information on the growth cycle of crops) is important
in the monitoring and classification of LU, where it can have a significant effect on
the accuracies of crop yield and acreage change. It controls the temporal changes
observed from remotely sensed data. The integration of space and time represent
crop growth in remote sensing. So, crop phenology contributes to the under-
standing and monitoring (e.g., spectral measurements) of crop type reorganization
and area measurement. Different crops (wheat, barley, cotton, corn, etc.) have a
clear and unmistakable spectral response exhibit and period of maximum green-
ness. This information or phenology can be used in the classification process to
accurately discriminate vegetation classes (Hoffer 1980 ).
Phenological knowledge (beside the spectral measurements) plays a critical role
in determining optimal acquisition dates for the selection of the remotely sensed
data for agricultural monitoring and classification. As, wheat can be easily
recognized from other crops and vegetation because of its greater Greenup,
that occurs earlier than for other crops. Crop phenology is generally divided into:
''(1) vegetative stage: is largely defined by the part of the growth cycle where the
crop develops and grows, starting emergence to tasseling; and (2) reproductive
stage: starts at anthesis and ends after maturity. For dry-land crops, several tran-
sitions are important in terms of management: emergence, tasseling and initiation
of senescence'' (Chen et al. 2008 ).
5.5.2 The Size of the Agriculture Holdings and Methods
of Water Supply/Spatial Considerations/Spatial Aspects
of Spectral Response Patterns
The questions related to spatial characteristics of the used data are: how much is
the size area concerned? Is it sufficient to classify only a sample of all the data, or
is it necessary to classify the all data for the whole coverage of the study area?
What format of results is needed (maps and/or tables)? If the needed format is a
map as a final product, then what scale and level of accuracy is needed? What are
the spatial characteristics of the agricultural features in comparison to the char-
acteristics of the used remotely sensed data (Hoffer 1980 )? And finally, what are
the spatial aspects of the spectral response patterns?
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