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Related Concept Videos

Areas Within Irregular Boundaries01:26

Areas Within Irregular Boundaries

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Calculating areas within irregular boundaries, such as along rivers or curved roads, is crucial in various fields, including surveying, engineering, and environmental management. Surveyors often begin by creating a traverse, a connected series of straight lines approximating the area's boundary. The coordinates of each traverse point are essential for calculating the enclosed area. The double meridian distance formula is a widely used technique for this purpose. This method utilizes the...
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Area Computation by the Alternative Coordinate Method01:24

Area Computation by the Alternative Coordinate Method

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The alternative coordinate method, also known as the Shoelace Formula, is a technique for determining the area of a traverse using Cartesian coordinates. This method relies on the sequential arrangement of x and y coordinates for each point of the shape, ensuring accuracy and ease of application.In this approach, each corner's x and y coordinates are listed as fractions, with the x-coordinate as the numerator and the y-coordinate as the denominator. These coordinates are arranged sequentially...
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Simpson’s Rule is a numerical integration method used to approximate the value of a definite integral when an exact antiderivative is difficult or impossible to obtain. The method estimates area by fitting a unique parabola through three equally spaced points on a curve and then integrating the resulting quadratic function over the interval. By using only a small number of sampled values, Simpson’s Rule provides an accurate approximation for many smoothly varying functions.A common...
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Midpoint Rule01:20

Midpoint Rule

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Approximating areas under curved boundaries is a common problem in applied mathematics, particularly when an exact calculation is difficult or impractical. One effective numerical method for this purpose is the Midpoint Rule, which provides an estimate of the area under a curve by using rectangular approximations over a specified interval.Description of the Midpoint RuleThe Midpoint Rule begins by dividing the given interval into a number of equal subintervals. For each subinterval, the...
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Area Problem01:26

Area Problem

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Determining the area of a region with straight edges is straightforward, as geometric formulas for rectangles, triangles, and polygons can be applied directly. However, traditional geometric methods are insufficient when a region has a curved boundary, such as the area under a function.fromThe area problem involves finding a systematic way to measure such regions. One approach to solving this problem is through approximation. Instead of attempting to compute the area exactly at the outset, the...
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Trapezoidal channels are widely used in irrigation systems due to their cost-effectiveness and efficiency in conveying water. Trapezoidal channels feature a flat bottom and sloping sides, making them stable and easier to construct compared to other shapes. The bottom width and side slope ratio are determined based on the required flow capacity and site conditions. The side slope is kept gentle for unlined channels to prevent soil erosion.Hydraulic parameters in channel design include the flow...
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Related Experiment Video

Updated: Feb 23, 2026

Leaf Area Index Estimation Using Three Distinct Methods in Pure Deciduous Stands
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Sub-pixel Area Calculation Methods for Estimating Irrigated Areas.

Prasad S Thenkabailc1, Chandrashekar M Biradar2, Praveen Noojipady3

  • 1International Water Management Institute, Colombo, Sri Lanka. p.thenkabail@cgiar.org.

Sensors (Basel, Switzerland)
|September 15, 2017
PubMed
Summary

This study introduces three practical methods to calculate sub-pixel irrigated areas (SPIAs) from coarse satellite data, improving accuracy over traditional full pixel methods. These new techniques offer more precise estimations of global and national irrigation extents.

Keywords:
IAF-GEEIAF-HRIIAF-SPDThigh-resolution imageryirrigated area fractionssub-pixel areassub-pixel de-composition technique

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Area of Science:

  • Remote Sensing
  • Geospatial Analysis
  • Agricultural Monitoring

Background:

  • Accurate mapping of irrigated areas is crucial for water resource management and food security.
  • Coarse-resolution satellite data often leads to overestimation of irrigated areas when treated as full pixels.
  • Existing methods for sub-pixel area estimation have limitations in accuracy and applicability.

Purpose of the Study:

  • To develop and demonstrate practical methods for computing sub-pixel areas (SPAs) from coarse-resolution satellite sensor data.
  • To compare the accuracy of novel SPA computation methods against established techniques and full pixel estimations.
  • To validate the utility of SPAs for national and global irrigation assessments.

Main Methods:

  • Developed three methods for computing irrigated area fractions (IAFs): Google Earth Estimate (IAF-GEE), High Resolution Imagery (IAF-HRI), and Sub-pixel Decomposition Technique (IAF-SPDT).
  • IAF-GEE utilizes very high-resolution imagery for total available irrigation area estimation.
  • IAF-SPDT employs a unique 2D brightness-greenness-wetness feature space for precise SPA determination.

Main Results:

  • The IAF-SPDT method showed results within 2% of the established IAF-HRI method for the Global Irrigated Area Map (GIAM).
  • Sub-pixel irrigated areas (SPIAs) derived from the new methods were significantly more accurate and had lower uncertainties than full pixel irrigated areas (FPIAs).
  • SPIAs provided a closer approximation to actual irrigated areas compared to FPIAs, which tended to grossly overestimate.

Conclusions:

  • The study highlights the significant value and importance of using sub-pixel areas over full pixel areas for accurate remote sensing-based land cover assessments.
  • The developed methods, particularly IAF-SPDT, offer innovative and practical solutions for computing SPAs from coarse satellite data.
  • Accurate SPIA estimations are vital for improving global and national irrigated area mapping and subsequent resource management decisions.