【遙感遙測】【2016】灌溉玉米田間土壤水分變化的遙感定量研究

本文為美國科羅拉多州大學（作者：Jeffrey Alan Siegfried）的碩士論文，共134頁。

農業是全球最大的水消費領域。隨著可用水資源壓力的增加，用更少的水生產更多的糧食變得至關重要。精確供水方法（如變數灌溉）所需的硬體技術在商業上是可以買到的。儘管如此，為這些系統制定及時、準確的處理技術仍然是不夠的。

光譜植被指數，特別是歸一化差異植被指數，常用於衡量作物活力及相關引數（如葉片含氮量和產量）。然而，迄今為止的研究很少涉及土壤溼度對指數的影響。用廉價紅外溫度計測量的冠層溫度也可以作為衡量水分的指標，但是目前利用這些資料的方法可能會很麻煩。因此，本研究的目的是確定

1）從多光譜衛星影像獲得的植被指數是否有助於量化灌溉玉米生產系統中的土壤水分變化特性

2）單個影像代表土壤水分狀況的時間段

3）確定同步測量作物冠層溫度和田間土壤水分張力；

4）瞭解任意作物冠層溫度應力閾值對土壤水分與作物冠層溫度關係的影響。

採用變數灌溉支點形成六個水處理區。每個區域都配備了一套張力計，安裝在20、45和75釐米深的地塊中心，此外，還有一個指向作物冠層的紅外溫度計用於監測水處理區的狀況。在每個處理區中，以估計蒸散量（ET）需求量的百分比進行供水：即40%、60%、80%、100%、120%和140%。從張力計收集的資料與對應於張力計地面位置的影像畫素以及同步的冠層溫度資料配對，分別進行了統計分析，以評估植被指數和冠層溫度是否代表多種作物生長階段的土壤水分。研究結果表明，歸一化差異植被指數可以量化作物生長期V6（6葉）（r2=0.850，p=0.009）和V9（9葉）（r2=0.913，p=0.003）作物生長期土壤水分張力的變化特性。結果表明，衛星植被指數可能有助於建立大尺度土壤水分變化的時間敏感性特徵。當與閾值相結合時，同步冠層溫度能夠量化生殖作物生長階段的土壤水分張力。進一步的研究是必要的，以調查額外的作物生長階段、更多的作物和其他來源的多光譜影像。未來的研究還需要評估變數灌溉管理的田間規模產量影響。

Agriculture is the largest consumer ofwater globally. As pressure on available water resources increases, the need toexploit technology in order to produce more food with less water becomescrucial. The technological hardware requisite for precise water deliverymethods such as variable rate irrigation is commercially available. Despitethat, techniques to formulate a timely, accurate prescription for those systemsare inadequate. Spectral vegetation indices, especially Normalized DifferenceVegetation Index, are often used to gauge crop vigor and related parameters(e.g. leaf nitrogen content and grain yield). However, research heretoforerarely addresses the influence of soil moisture on the indices. Canopytemperature measured using inexpensive infrared thermometers could also serveas an indicator of water stress, but current methods which exploit the data canbe cumbersome. Therefore, the objectives of this study were to determine 1) ifvegetation indices derived from multispectral satellite imagery could assist inquantifying soil moisture variability in an irrigated maize production system2) the period of time which a single image is representative of soil moistureconditions 3) to determine the relationship between synchronous measurements ofcrop canopy temperature and in-field soil moisture tension, and 4) tounderstand the influence of discretionary crop canopy temperature stressthresholds on the relationship between soil moisture tension and crop canopytemperature. A variable rate irrigation pivot was used to form six watertreatment zones. Each zone was equipped with both a set of tensiometersinstalled in the center of the plots at 20, 45, and 75cm depths and an infraredthermometer pointed into the crop canopy to individually monitor conditions inthe water treatment zones. Water was applied for each treatment as a percentageof the estimated evapotranspiration (ET) requirement: i.e., 40, 60, 80, 100,120, and 140 percent of the ET. Data collected from tensiometers was pairedwith the image pixels corresponding to the ground location of the tensiometersand with the synchronous canopy temperature data. Statistical analysis wasperformed separately to assess whether vegetation indices and canopytemperature are representative of soil moisture at several crop growth stages.Findings from this study indicate that Red Edge Normalized DifferenceVegetation Index could quantify variability of soil moisture tension at V6 (sixleaf) (r2 = 0.850, p = 0.009) and V9 (nine leaf) (r2 = 0.913, p = 0.003) cropgrowth stages. Results suggest that satellite-derived vegetation indices may beuseful for creating time-sensitive characterizations of soil moisturevariability at large field-scales. When integrated with a stress threshold,synchronous canopy temperature was able to quantify soil moisture tension withsome success during the reproductive crop growth stages. Further study isnecessary to investigate additional crop growth stages, more crops, and othersources of multispectral imagery. Future studies are also needed to evaluatefield-scale yield implications of variable rate irrigation management.

1. 用多光譜衛星影像定量分析田間土壤水分變化特性
2. 灌溉玉米田間土壤水分變化的紅外測溫研究

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