Merging Alternate Remotely-Sensed Soil Moisture Retrievals Using a Non-Static Model Combination Approach
"> Figure 1
<p>Locations of 124 ground stations from 10 networks used for the comparison with combined products.</p> "> Figure 2
<p>Schematic diagram for dynamic linear combination. T denotes the period defined by the window (<span class="html-italic">i.e</span>., T = (t − N/2):(t + N/2)). Therefore, a bold symbol that has T as its subscript means a vector in the period T, and a non-bold symbol with t as the subscript represents a value at the point in time <span class="html-italic">t</span>.</p> "> Figure 3
<p>Results from experiments that uses ERA-Interim as the reference for various window sizes, N60, N90 and N120. Each panel shows the R between the reference and (<b>a</b>) JAXA; (<b>b</b>) LPRM; (<b>c</b>) static; (<b>d</b>) N60; (<b>e</b>) N90 and (<b>f</b>) N120; the more bluish colours in the maps indicate higher R against the reference; the overall performance for the various scenarios is summarized in the boxplot (<b>g</b>).</p> "> Figure 4
<p>Comparison between combined soil moisture products. For ERA-Interim as the reference, (<b>a</b>) The differences in R between the static and N60 products against the reference (<span class="html-italic">i.e</span>., R of N60 minus R of static) and (<b>b</b>) the mean weights that were used for the dynamic combination using the reference over the two-year study period; (<b>c</b>) and (<b>d</b>) show corresponding results with (<b>a</b>) and (<b>b</b>) when using MERRA-Land as the reference.</p> "> Figure 5
<p>Results from the simulation experiment. (<b>a</b>) The x-axis indicates Euclidean distances (ξ) calculated by Equation (7), representing the qualities of the parent products, and the y-axis, <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>d</mi> <mi>y</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics> </math> or <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>s</mi> <mi>t</mi> <mi>a</mi> </mrow> </msub> </mrow> </semantics> </math>. The dashed two lines present the linear regression of all results from the dynamic and static combinations, respectively; (<b>b</b>) The x-axis indicates N sizes, the y-axis differences between <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>d</mi> <mi>y</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>s</mi> <mi>t</mi> <mi>a</mi> </mrow> </msub> </mrow> </semantics> </math> (<span class="html-italic">i.e</span>., <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>d</mi> <mi>y</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics> </math> − <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>s</mi> <mi>t</mi> <mi>a</mi> </mrow> </msub> </mrow> </semantics> </math>).</p> "> Figure 6
<p>(<b>a</b>) Box plots showing combination performances against <span class="html-italic">in situ</span> measurements with the N60 and the two references. The labels on the x-axis indicate parent or statically-/dynamically-combined products with the references, and the y-axis R between the product and the <span class="html-italic">in situ</span> measurements. The value in each box is the mean of R. Comparison against <span class="html-italic">in situ</span> measurements from the ISMN for dynamically combined products using the N60 and (<b>b</b>) ERA-Interim and (<b>c</b>) MERRA-Land as the reference, respectively. The x-axis presents R between a dynamic product and the <span class="html-italic">in situ</span> measurements from a station, the y-axis R between a static product and the <span class="html-italic">in situ</span> measurements.</p> "> Figure 7
<p>Dynamic and static combination results using MERRA-Land as the reference at (<b>a</b>) Sandy Ridge station in Soil Climate Analysis Network and (<b>b</b>) Sandstone-6-W station in U.S. Climate Reference Network. Each panel shows static/dynamic weights (<b>top</b>), as well as time series of statically- and dynamically-combined soil moisture products (<b>bottom</b>).</p> "> Figure 8
<p>Combination performances with the quality of parent products and reference against <span class="html-italic">in situ</span> measurements. (<b>a</b>) ERA-Interim; (<b>b</b>) MERRA-Land. The x-axis for each panel presents the Euclidean distances (ξ) calculated by Equation (8), and the y-axis <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>s</mi> <mi>i</mi> <mi>t</mi> <mi>u</mi> <mo>−</mo> <mi>s</mi> <mi>t</mi> <mi>a</mi> </mrow> </msub> </mrow> </semantics> </math> or <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>s</mi> <mi>i</mi> <mi>t</mi> <mi>u</mi> <mo>−</mo> <mi>d</mi> <mi>y</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics> </math>. Linear regression lines represent the tendencies of both cases.</p> "> Figure 9
<p>Combination performances with reference quality against <span class="html-italic">in situ</span> measurements. The x-axis presents R between <span class="html-italic">in situ</span> measurements and the references (<math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>s</mi> <mi>i</mi> <mi>t</mi> <mi>u</mi> <mo>−</mo> <mi>r</mi> <mi>e</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics> </math>), the y-axis R between <span class="html-italic">in situ</span> measurements and statically-/dynamically-combined products (<math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>s</mi> <mi>i</mi> <mi>t</mi> <mi>u</mi> <mo>−</mo> <mi>s</mi> <mi>t</mi> <mi>a</mi> </mrow> </msub> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>s</mi> <mi>i</mi> <mi>t</mi> <mi>u</mi> <mo>−</mo> <mi>d</mi> <mi>y</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics> </math>). Linear regression lines are added for representing the average tendencies of both cases.</p> ">
Abstract
:1. Introduction
2. Data and Processing
2.1. Data
2.1.1. Remotely-Sensed Soil Moisture Products
2.1.2. Reanalysis Soil Moisture Products
2.1.3. In Situ Soil Moisture Measurements and Ancillary Data
2.2. Data Preprocessing
3. Methodology
3.1. Static Linear Combination
3.2. Dynamic Linear Combination
4. Results
4.1. Global Data Combination with Various Scenarios
4.2. A Simulation Experiment
4.3. Comparison against in Situ Observations
4.4. Influence of the Quality of the Parent Products and Reference
5. Discussion
6. Conclusions
Supplementary Materials
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Data Source | Dataset | Temporal Resolution | Spatial Resolution | Units |
---|---|---|---|---|
AMSR2-JAXA | Level 3 geophysical parameter SMC | Daily | 0.25° | m3/m3 |
AMSR2-LPRM | Level 3 Surface Soil Moisture X-band | Daily | 0.25° | m3/m3 |
AMSR2-LPRM | Vegetation optical depth C-band | Daily | 0.25° | - |
AMSR2 | Scan time | Daily | 0.25° | s |
ERA-Interim | Soil water contents Level 1 0–0.07-m depth | 6 h | 0.25° | m3/m3 |
ERA-Interim | Soil temperature Level 1 0–0.07-m depth | 6 h | 0.25° | K |
MERRA-Land | Top soil layer soil moisture consent SFMC | Hourly | 0.25° Resampled | m3/m3 |
ISMN | In situ measured soil moisture from 124 stations in 10 networks | Hourly | Point | m3/m3 |
ESA CCI | Topographic complexity, wetland fraction | - | 0.25° | % |
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Kim, S.; Parinussa, R.M.; Liu, Y.Y.; Johnson, F.M.; Sharma, A. Merging Alternate Remotely-Sensed Soil Moisture Retrievals Using a Non-Static Model Combination Approach. Remote Sens. 2016, 8, 518. https://doi.org/10.3390/rs8060518
Kim S, Parinussa RM, Liu YY, Johnson FM, Sharma A. Merging Alternate Remotely-Sensed Soil Moisture Retrievals Using a Non-Static Model Combination Approach. Remote Sensing. 2016; 8(6):518. https://doi.org/10.3390/rs8060518
Chicago/Turabian StyleKim, Seokhyeon, Robert M. Parinussa, Yi Y. Liu, Fiona M. Johnson, and Ashish Sharma. 2016. "Merging Alternate Remotely-Sensed Soil Moisture Retrievals Using a Non-Static Model Combination Approach" Remote Sensing 8, no. 6: 518. https://doi.org/10.3390/rs8060518