A review of spatial downscaling of satellite remotely sensed soil moisture

Satellite remote sensing technology has been widely used to estimate surface soil moisture. Numerous efforts have been devoted to develop global soil moisture products. However, these global soil moisture products, normally retrieved from microwave remote sensing data, are typically not suitable for regional hydrological and agricultural applications such as irrigation management and flood predictions, due to their coarse spatial resolution. Therefore, various downscaling methods have been proposed to improve the coarse resolution soil moisture products. The purpose of this paper is to review existing methods for downscaling satellite remotely sensed soil moisture. These methods are assessed and compared in terms of their advantages and limitations. This review also provides the accuracy level of these methods based on published validation studies. In the final part, problems and future trends associated with these methods are analyzed

Evaluation of sampling techniques to characterize topographically-dependent variability for soil moisture downscaling

2013 Summer.Includes bibliographical references.Soil moisture patterns are an important consideration in many catchment-scale hydrologic applications. Unfortunately, estimating soil moisture patterns at resolutions that are appropriate for these applications (e.g., grid cells with a linear dimension of 10 to 50 m) is difficult. Downscaling methods can be used to estimate catchment-scale soil moisture patterns from coarser resolution estimates or spatial average soil moisture values. These methods usually infer the fine-scale variability in soil moisture using variations in ancillary variables like topographic attributes that have relationships to soil moisture. Previously, such relationships have been observed in catchments using soil moisture observations taken on uniform grids at hundreds of locations on multiple dates, but collecting data in this manner limits the applicability of this approach. The objective of this paper is to evaluate the effectiveness of two strategic sampling techniques for characterizing the relationships between topographic attributes and soil moisture for the purpose of constraining downscaling methods. The strategic sampling methods considered are conditioned Latin hypercube sampling (cLHS) and stratified random sampling (SRS). Each sampling method is used to select a limited number of locations and/or dates for soil moisture monitoring at three catchments with detailed soil moisture datasets (Tarrawarra, Satellite Station, and Cache la Poudre). These samples are then used to calibrate two available downscaling methods, and the effectiveness of the sampling methods is evaluated by the ability of the downscaling methods to reproduce the known soil moisture patterns at the catchments. The results show that cLHS and SRS can characterize the relationships between soil moisture and ancillary topographic variables with many fewer locations and dates than previously used. For example, when the number of locations for soil moisture monitoring is reduced by 82-90% and these locations are only monitored on 3 dates, the explanatory power of the downscaling methods frequently only reduces by less than 50%. Furthermore, both strategic sampling methods can substantially outperform random sampling when the number of samples is limited

Reproductive ecology of interior least tern and piping plover in relation to Platte River hydrology and sandbar dynamics

Investigations of breeding ecology of interior least tern (Sternula antillarum athalassos) and piping plover (Charadrius melodus) in the Platte River basin in Nebraska, USA, have embraced the idea that these species are physiologically adapted to begin nesting concurrent with the cessation of spring floods. Low use and productivity on contemporary Platte River sandbars have been attributed to anthropomorphically driven changes in basin hydrology and channel morphology or to unusually late annual runoff events. We examined distributions of least tern and piping plover nest initiation dates in relation to the hydrology of the historical central Platte River (CPR) and contemporary CPR and lower Platte River (LPR). We also developed an emergent sandbar habitat model to evaluate the potential for reproductive success given observed hydrology, stage–discharge relationships, and sandbar height distributions. We found the timing of the late-spring rise to be spatially and temporally consistent, typically occurring in mid-June. However, piping plover nest initiation peaks in May and least tern nest initiation peaks in early June; both of which occur before the late spring rise. In neither case does there appear to be an adaptation to begin nesting concurrent with the cessation of spring floods. As a consequence, there are many years when no successful reproduction is possible because emergent sandbar habitat is inundated after most nests have been initiated, and there is little potential for successful renesting. The frequency of nest inundation, in turn, severely limits the potential for maintenance of stable species subpopulations on Platte River sandbars. Why then did these species expand into and persist in a basin where the hydrology is not ideally suited to their reproductive ecology? We hypothesize the availability and use of alternative off-channel nesting habitats, like sandpits, may allow for the maintenance of stable species subpopulations in the Platte River basin

Investigating whooping crane habitat in relation to hydrology, channel morphology and a water-centric management strategy on the central Platte River, Nebraska

The Flow-Sediment-Mechanical approach is one of two management strategies presented in the Platte River Recovery Implementation Program's (Program) Adaptive Management Plan to create and maintain suitable riverine habitat (≥200 m wide unobstructed channels) for whooping cranes (Grus americana). The Program's Flow-Sediment-Mechanical management strategy consists of sediment augmentation, mechanical vegetation clearing and channel widening, channel consolidation, and short duration high flow releases of 142–227 m3/s for three to five days in two out of three years in order to increase the unvegetated width of the main channel and, by extension, create and maintain suitable habitat for whooping crane use. We examined the influence of a range of hydrologic and physical metrics on total unvegetated channel width (TUCW) and maximum unobstructed channel width (MUOCW) during the period of 2007–2015 and applied those findings to assess the performance of the Flow-Sediment-Mechanical management strategy for creating and maintaining whooping crane roosting habitat. Our investigation highlights uncertainties that are introduced when exploring the relationship between physical process drivers and species habitat metrics. We identified a strong positive relationship between peak flows and TUCW and MUOCW within the Associated Habitat Reach of the central Platte River. However, the peak discharge magnitude and duration needed to create highly favorable whooping crane roosting habitat within our study area are much greater than short duration high flow releases, as currently envisioned. We also found disking in combination with herbicide application to vegetated portions of the channel are effective for creating and maintaining highly favorable unobstructed channel widths for whooping cranes in all but the very driest years. As such, resource managers could prioritize the treatment of mid-channel islands that are vegetated to increase the suitability of roosting habitat for whooping cranes

Drought monitoring using high resolution soil moisture throughmulti-sensor satellite data fusion over the Korean peninsula

Droughts, typically caused by the deficiencies of precipitation and soil moisture, affect water resources and agriculture. As soil moisture is of key importance in understanding the interaction between the atmosphere and Earth???s surface, it can be used to monitor droughts. In this study, a High resolution Soil Moisture Drought Index (HSMDI) was proposed and evaluated for meteorological, agricultural, and hydrological droughts. HSMDI was developed using the 1 km downscaled soil moisture data produced from the Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E) from 2003 to 2011 (March to November) over the Korean peninsula. Seven products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measuring Mission (TRMM) satellite sensors were used to downscale AMSR-E soil moisture based on random forest machine learning. The downscaled 1 km soil moisture was correlated well with both in situ and AMSR-E soil moisture with the mean coefficient of determination (R2) of 0.29 and 0.59, respectively. The Standardized Precipitation Index (SPI) with time scales from 1 to 12 months, crop yields (for sesame, highland radish, and highland napa cabbage) and streamflow data were used to validate HSMDI for various types of droughts. The results showed that HSMDI depicted meteorological drought well, especially during the dry season, with a similar pattern with the 3-month SPI. However, the performance fluctuated a bit during the wet season possibly due to the limited availability of optical sensor data and heterogeneous land covers around the stations. HSMDI also showed high correlation with crop yield data, in particular the highland radish and napa cabbage cultivated in non-irrigated regions with a mean R2 of 0.77. However, HSMDI did not monitor streamflow well for hydrological drought presenting a various range of correlations with streamflow data (from 0.03 to 0.83).clos