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A brief introduction to the TOPS-SIMS web interface:


About this dataset
Viewing data
Finding a location
Selecting a date
Querying the dataset
Downloading data
Downloading seasonal ETcb data
More information


About this dataset:

The primary objective of the TOPS-SIMS project is to develop new satellite-derived datasets and tools designed to support agricultural producers and water managers in optimizing management of irrigation and agricultural water supplies. These datasets were developed by the Ecological Forecasting Lab at NASA Ames Research Center in collaboration with the California Department of Water Resources, California State University at Monterey Bay, California State University Fresno, and the USDA Agricultural Research Service, and with support from the NASA Applied Sciences Program. For more information about the project, please see the About page.

These datasets are distributed for research, demonstration, and evaluation purposes only. The datasets are currently under review and should be considered provisional at this time.

Datasets available through the TOPS-SIMS web interface include:

  • NDVI: The normalized difference vegetation index (NDVI) provides a measure of vegetation photosynthetic capacity (for more information about NDVI, please see this overview. The NDVI data layer is provided to assist growers and irrigation consultants in evaluating crop canopy conditions and monitoring variability in crop condition. NDVI is sensitive to all green vegetation present in the field, including the crop plus any underlying cover-crop or weeds

  • NDVI gap-filled: Due to a hardware failure on the Landsat 7 satellite, stripes of data are missing in some of the satellite scenes used as inputs to SIMS. The 'NDVI gap-filled' layer uses a moving window gap-filling algorithm to estimate these missing values. The algorithm fills >90% of the missing values within 0.1 NDVI units.

  • Fc: Fractional cover is the proportion of ground area that is covered with green vegetation as viewed from directly overhead.

  • Kcb: Kcb is the basal crop coefficient used to calculate the ETcb, and is calculated from the Fc using relationships developed by USDA and NASA. Kcb represents conditions for an unstressed (well-watered) crop on a dry soil surface. Kcb is insensitive to crop water stress except for episodes of chronic water shortage that cause stunted plant growth. Kcb is largely insensitive to evaporation from wet soil surface. Kcb, as calculated by SIMS, assumes "standard" sub-humid climate/weather conditions, specifically with average daily wind speed below ~5 mph and relative humidity above 45%. Additional corrections are available in the agronomic literature and should be applied for "non-standard" climate/weather conditions. The SIMS Kcb incorporates the contribution of all green vegetation present in the field.

  • ETcb: ETcb is basal crop evapotranspiration calculated via a standard crop coefficient approach, ETcb = ETo * Kcb. Reference evapotranspiration (ETo) observations are automatically retrieved from the Spatial CIMIS archive of the California Irrigation Management Information System (CIMIS). Components of ETcb include potential (unstressed) crop transpiration and diffuse (sub-surface) soil evaporation. As above, ETcb does not include direct evaporation from any wet soil surface. Also as above, the SIMS ETcb assumes "standard" sub-humid climate, and represents the combined contribution of all green vegetation present in the field (crop, cover crop, weeds).

Viewing and navigating:

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To select SIMS data for viewing, use the 'layer manager' to select the NDVI, NDVI gap-filled, Fc, Kcb, or the ETcb data layer. In addition, Google Streets, Google Terrain, and Google Satellite base layers are available. To view these Google base layers, the other SIMS 'overlay' data layers must first be unchecked. If the layer manager is closed, click on the blue and white button in the upper right corner of the map window. slc img

SIMS Layer Manager

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Pan – depress and hold mouse button, or use pan/zoom bar

Zoom – use the zoom bar

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Finding a location:

To search for a field, vineyard, orchard or other location of interest, use the 'Go to:' search field. Type in the street address (most farm roads should work fine) and city and state, road intersection, or the latitude and longitude. When entering the lat/long coordinates, be sure to enter the latitude first, followed by the longitude preceded with a minus sign ('-'), as shown in the example below. Note: Searching for a location will automatically execute a query for the location of interest.

SIMS Location Search

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An orange circle will appear at the selected active location.

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The location of the cursor is also displayed in the lower right hand corner of the map:

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Selecting a date:

To view data for a date of interest, click within the 'Select Date' window and use the calendar to select the date and year of interest. Data are currently available for 2010-2012.

Querying and downloading:

To query the dataset, briefly click (or left-click) on any point on the map. A query results window will return the current values for all available data layers at that location, along with the date, lat/long, and general crop type. A corresponding time-series showing the annual progression of the data layers can be displayed (select "graph") or downloaded as comma-separated-values (select "csv") for import to Notepad, Wordpad, other text editors, MS Excel, and other spreadsheet tools. To pan across the map, click and hold down the mouse button.

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Downloading data:

To download the results of the query, click the 'Download as CSV' link in the query results window. This will open a dialog window that will allow the user to save the results as a CSV (comma separated value) format file. CSV files can be opened with Notepad, Wordpad, other text editors, MS Excel, and other spreadsheet tools.

Seasonal ETcb compilation:

The estimates of ETcb provided by the SIMS interface are estimates of basal crop evapotranspiration, which includes plant transpiration (productive water use) plus a small diffusive evaporation component from sub-surface soil water. ETcb does not include evaporation directly from the soil surface resulting from irrigation events or precipitation. ETcb also does not account for transpiration reduction associated with crop water stress resulting from intentional or deficit irrigation, unless stress diminishes the canopy cover. As such, the SIMS ETcb should be considered to represent the biological demand (water use) of the crop under normal, well watered conditions. Finally, SIMS does not differentiate between crop and other vegetation that might be present in the field, such as a cover-crop or weeds. Therefore, the ETcb estimate includes transpiration contributions by all vegetation components, leading to over-statement of crop water demand in cases where significant non-crop vegetation is present.

To download the seasonal ETcb for a location of interest, first zoom to a level at which individual fields can be clearly seen. Next, type in the address, nearest intersection, or latitude and longitude for a field of interest. Adjust the map so that the field boundaries can be clearly seen. Next, click on the center of the field, on a location which is representative of the overall field condition. Once the query result loads, click on the 'Download as CSV' link to save the file. Open the file in Excel or another spreadsheet program. Delete data prior to the planting date, and after the harvest date, and calculate the sum of the remaining entries.

More information:

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