Influence of Landsat Revisit Frequency on Time-Integration of Evapotranspiration for Agricultural Water Management

The objective of this study was to explore the improvement in accuracy of estimates for evapotranspiration (ET) over complete growing seasons and monthly periods, when more frequent Landsat imagery is made available. Conversely, we explored the reduction in accuracy in ET estimates when frequency of Landsat imagery was reduced. The study was implemented by conducting a series of METRIC applications for two Landsat WRS path overlap areas, one in southern Idaho (paths 39 and 40) during 2000, and a second one in Nebraska (paths 29 and 30) during 2002, years when two fully functioning satellites, Landsat 5 and Landsat 7, were in orbit. The results indicated that high frequency imagery provided by two satellites covering a WRS path overlap was more able to capture the impacts of rapid crop development and harvest, and evaporation associated by wetting events. That data set simulated a nominal four-day revisit time. Three-simulated 16-day revisit data sets created using a single Landsat series for a single path were unable to produce monthly and growing season ET due to the lack of sufficient number of images to even begin the time-integration process. This emphasizes the need to maintain two Landsat satellites in orbit and the high value of four-day revisit times. Limiting the data set to one path and two satellites (eight-day revisit) underestimated growing season ET accordingly by about 8% on average. Error in monthly ET was relatively high when image availability was limited to that for an eight-day revisit. This is due to the importance of timing of images to identify key inflection points in the ETrF curves and to capture special events such as wetting events from irrigation and rain or from water stress or cuttings, as in the case of forage crops. Results suggest that a four-day revisit time as represented by the full-run (run 1) of our analysis provides robustness in the development of time-integrated ET estimates over months and growing seasons, and is a valuable backstop for mitigation of clouded images over extended periods

Ground water and surface water under stress

Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.Includes bibliographical references.The METRIC evapotranspiration (ET) estimation model was applied using MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images in New Mexico to evaluate the applicability of MODIS images to ET estimation and water resources management. With the coarse resolution of MODIS (approximately 1km thermal resolution), MODIS was not found to be suitable for field-scale applications. In project and regional scale applications, MODIS has potential to contribute to ET estimation and water resources management. MODIS based ET maps for New Mexico were compared with Landsat based results for 12 dates. Average ET calculations using MODIS and Landsat applications were similar, indicating that MODIS images can be useful as an ET estimation tool in project and regional scale applications

Change of Behavior of \u3cem\u3eBos grunniens\u3c/em\u3e in the Alpine Rangeland in the Eastern Tibetan Plateau

Over 6 million yaks (Bos grunniens) are grazed in the alpine rangelands of the eastern Tibetan Plateau in Qinghai Province, China. Degradation of rangelands has been caused by increased numbers of domestic animals following the rise of the human population. In our previous study in northern and southern sites of Tibetan Plateau in Qinghai Province from 2003 to 2006, behavior of yaks and chemical composition of the faeces (Hasegawa et al. 2006; Hasegawa et al. 2008) and vegetation (Li et al. 2006; Song et al. 2006) were investigated and compared between the two sites, and it was suggested that the material circulation was lower and deterioration of rangeland was greater in the former than in the latter. In this study, behavioral observations of yaks in alpine rangeland of Yushu National Ranch from 2004 to 2012 were carried out to estimate the change of rangeland condition in the southern site of Tibetan Plateau

An Ecological Monitoring of the Plateau Pika and Its Impact on Grassland–An Experiment in the Yushu District, Qinghai Province of China

The plateau pika (Ochotona curzoniae; see Fig.1 for photo) is a small mammal that lives in the alpine grasslands of the Tibetan Plateau. There are several uncertainties existing in the ecological behavior of the plateau pika and its impact on the alpine grasslands, and this impact has long been a subject under discussion. The mammal will have created both positive and negative impacts to the plateau environment and the alpine ecology. In China the plateau pika is regarded as a pest and has been a target of control or extermination because it is a competitor with livestock for food.It also putatively destroys fragile high-altitude grasslands and accelerates the spread of deserts. On the other hand, some scientists have believed that the plateau pika is important for alpine grasslands and the ecology, by tilling the soil and also by functioning as a keystone species for biodiversity of the plateau. This paper summarizes a part of the pika’s behavior identified through the experiment conducted during the summer of 2012 in the Qinghai-Tibetan Plateau, China

Relationship between Soil Chemical and Physical Properties and Vegetation in the Latest Decade of Alpine Grasslands of Southern Qinghai, China

The Tibetan Plateau is one of the most important ecosystems in the world (Yang et al. 2009), particularly because of the global importance of its climate (Tian et al. 2008; Wang et al. 2008). Grassland ecosystems on the plateau are sensitive to global change, because the plateau is located in marginal land areas where the growth and distribution of plants depend heavily on local climatic conditions (Zhang et al. 1996). The alpine grassland of Qinghai Province in China has been traditionally used for extensive grazing by sheep and yak (Bos grunniens), but is now degraded from overgrazing. This study investigated the relationship between soil chemical and physical properties and vegetation of alpine grasslands of southern Qinghai, China

Paddy Rice Double-Cropping Field Monitoring via Vegetation Indices with Limited Ground Data—A Case Study for Thapanzeik Dam Irrigation District in Myanmar

This study investigated two popular satellite-derived vegetation indices (VIs), MODIS NDVI and EVI, as tools for monitoring crop growth at the Thapanzeik Dam irrigation district in Myanmar, where quality ground data are difficult to obtain. The time-series analysis for seasonal peak VIs presented a considerable improvement in paddy cultivation during 2001–2020 in the irrigation district during summer and monsoon. Fields outside the district had a much lower improvement ratio. Within the irrigation district, a canal with limited water supply was identified via peak and average VIs evaluation. The evaluation of precipitation impact on crop growth demonstrated an opposite impact on crop growth in summer and monsoon cultivations. Water is one of the limiting factors in summer in the irrigation district; thus, precipitation improves water conditions. However, water is not the limiting factor in monsoon; thus, extra water from precipitation, both hydraulically and meteorologically, negatively impacts crop growth. Compared to NDVI, EVI better captured crop growth in densely vegetated surfaces. Meanwhile, information degradation might have occurred with 250 m EVI, using 500 m blue-band reflectance as an input. Thus, the best vegetation index to use depends on the purpose of monitoring and the site situation

Ground water and surface water under stress

Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.Includes bibliographical references.This paper presents a procedure to estimate actual evapotranspiration (ET) using a satellite-derived vegetation index. Actual ET is computed in a traditional manner using the crop coefficient (Kc) and reference ET (ETref) procedure (i.e., ET = Kc x ETref) with Kc estimated from the satellite-based NDVI. This study calibrated relationships between Kc and NDVI using satellite-based ET determined by surface energy balance. This unique approach enables calibration of the Kc vs NDVI equations using large numbers of sampled fields (in this case, more than 3000). Thus the calibration represents a regional average Kc estimate. The study was conducted for alfalfa, beans, sugar beet, corn, potatoes, and small grain crops, which are the major crops in southern Idaho. Estimation accuracy for ET was statistically evaluated. Average error of seasonal ET was within 5 percent of the energy balance (EB) determined ET for most crop types. Error in seasonal ET from individual fields is expected to be within 10 percent. NDVI based ET was compared with lysimeter measurements of ET from grass and sugar beets. The seasonal error of the NDVI based method was only 2 percent for grass and 6 percent for the sugar beets, as compared to lysimeter measurements. Statistical accuracy assessments suggest that NDVI based ET estimation can be a robust, simple and inexpensive tool to estimate ET from irrigated agricultural crops with reasonable good accuracy

Application of MODIS Land Products to Assessment of Land Degradation of Alpine Rangeland in Northern India with Limited Ground-Based Information

Land degradation of alpine rangeland in Dachigam National Park, Northern India, was evaluated in this study using MODerate resolution Imaging Spectroradiometer (MODIS) land products. The park has been used by a variety of livestock holders. With increasing numbers of livestock, the managers and users of the park are apprehensive about degradation of the grazing land. However, owing to weak infrastructure for scientific and statistical data collection and sociopolitical restrictions in the region, a lack of quality ground-based weather, vegetation, and livestock statistical data had prevented scientific assessment. Under these circumstances, the present study aimed to assess the rangeland environment and its degradation using MODIS vegetation, snow, and evapotranspiration products as primary input data for assessment. The result of the analysis indicated that soil water content and the timing of snowmelt play an important role in grass production in the area. Additionally, the possibility of land degradation in heavily-grazed rangeland was indicated via a multiple regression analysis at a decadal timescale, whereas weather conditions, such as rainfall and snow cover, primarily explained year-by-year differences in grass production. Although statistical uncertainties remain in the results derived in this study, the satellite-based data and the analyses will promote understanding of the rangeland environment and suggest the potential for unsustainable land management based on statistical probability. This study provides an important initial evaluation of alpine rangeland, for which ground-based information is limited