The Crop-CASMA data are offered as 9 kilometer and 1 kilometer raster data. Currently, there are several soil moisture data products and vegetative indices offered as detailed below and at <https://nassgeo.csiss.gmu.edu/Crop-CASMA-User/user/data/>.
Soil Moisture Data Products
This application disseminates the following NASA data products and their derivative data products.
NASA SMAP level 4 data including
- SMAPSurface 9km (every 3 hour)
- SMAPRootzone 9km (every 3 hour)
NASA SMAP level 4 derivative data products:
- SMAPSurface 9km (daily, weekly)
- SMAPRootzone 9km (daily, weekly)
- SMAPSurface 9km -- Anomaly (daily, weekly)
- SMAPRootzone 9km -- Anomaly (daily, weekly)
Categorized Soil Moisture Condition Data Converted from NASA SMAP level 4 derivative data products:
- SMAPSurface 9km -- Categorical (weekly)
- SMAPRootzone 9km -- Categorical (weekly)
NASA 1km High Resolution Soil Moisture data products Derived from SMAP, MODIS Land Surface Temperature and Soil Texture Data (NASA 1km SM Data):
- SM Surface 1km (weekly composite)
- SM Surface 1km (3day composite)
- SM Surface 1km (daily)
Derivative Data Products from NASA 1km SM Data:
- SM Surface 1km -- Anomaly (weekly)
- SM Surface 1km - Categorical (weekly)
Crop Vegetation Index Data Products
Normalized Difference Vegetation Index (NDVI) Products
- CROP-CASMA can provide daily and weekly NDVI products from 2000.
Vegetation Condition Index (VCI) Products
- Represent the weather condition or the vegetation condition. Currently CROP-CASMA can provide weekly VCI products from 2000.
Mean Vegetation Condition Index (MVCI) Products
- Represent the deviation of the vegetation to "normal" vegetation or multiple-year mean. Currently CROP-CASMA can provide on-demand weekly MVCI products from 2000.
The product and attribute descriptions below can be found online at <https://nassgeo.csiss.gmu.edu/Crop-CASMA-User/user/references/>.
NASS Top and Sub Soil:
-Top Soil (surface soil) - defined as the top 6 inches (approximately 15.25 centimeters).
-Sub Soil (rootzone soil) - defined as the top 3 feet (approximately 0.9 meters).
NASA Remotely Sensed Surface Soil and Rootzone Soil (SMAP Soil Moisture):
-Surface soil - defined as the top 2 inches (5 centimeters).
-Rootzone Soil - defined as the top 3.2 feet (approximately 1 meter).
Measure of NASA Soil Moisture:
The NASA SMAP 9km level-4 soil moisture and 1km soil moisture measurements are volumetric soil moisture (i.e. volumetric water content in the soil). It is simply the ratio of water volume to soil volume.
USDA/NASS Top and Sub-Soil Moisture Conditions (Categorical Assessment):
-Very Short - Soil moisture supplies are significantly less than what is required for normal plant development. Growth has been stopped or nearly so and plants are showing visible signs of moisture stress. Under these conditions, plants will quickly suffer irreparable damage.
-Short - Soil dry. Seed germination and/or normal crop growth and development would be curtailed.
-Adequate - Soil moist. Seed germination and/or crop growth and development would be normal or unhindered.
-Surplus - Soil wet. Fields may be muddy and will generally be unable to absorb additional moisture. Young developing crops may be yellowing from excess moisture.
Soil Moisture Anomaly
The soil moisture anomaly (SMA) in CropCASMA is a measure of deviation of the current soil moisture value from the "normal" soil moisture level, which is represented by a historical average soil moisture value (from 2015 to current). The SMA of a given location is defined by the following formula:
SMA= SM-SMm/SMm×100%
where SM and $\text{SM}_{m}$ denote current soil moisture value and the historical average soil moisture value of a given location.
NDVI - Normalized Difference Vegetation Index
Normalized Difference Vegetation Index (NDVI) is defined as follows:
NDVI= NIR-Red/NIR+Red
where Red and NIR stand for the spectral reflectance measurements acquired in the red (visible) and near-infrared bands, respectively. The NDVI value falls in [-1, 1] range.
In Crop-CASMA, the Surface Reflectance Daily L2G Global 250m data of MODIS are selected for the NDVI calculation. The L2G product has two bands -- Band~1~ (620-670 nm) and Band~2~ (841-876 nm), which represent red and near-infrared band respectively. To reduce file size, the real NDVI values are converted from in the range of [-1, 1] to integers in [0, 250]. Therefore, the daily NDVI in Crop-CASMA is rescaled as follows:
NDVI= Band2-Band1/Band2+Band1×125+125
The rescaled data are in the range of [0, 250].
VCI - Vegetation Condition Index
The Vegetation Condition Index (VCI) compares the current NDVI to the minimum historical NDVI value observed in the same period in previous years. It indicates where the currently observed NDVI value is situated between the historical extreme values (minimum and maximum) relatively. The VCI is defined by the following equation:
VCI= NDVI-NDVImin/NDVImax+NDVImin*250
where NDVI is the value at a given pixel, NDVI~min~ is the minimum value across multiple years at that pixel, NDVI~max~ is the maximum across the same period. It should be indicated that the data given in the equation is also rescaled to [0, 250] in order to reduce the file size.
MVCI - Mean Vegetation Condition Index
Mean Vegetation Condition Index (MVCI) represents the deviation of the vegetation condition from the "normal" vegetation condition, which is represented by NDVI historical average value. Mean Vegetation Condition Index is theoretically defined by the following equation:
mm= NDVI-NDVIm/NDVIm×100
where NDVI represents the current vegetation condition and NDVI~m~ represents the mean value of historical NDVI values. Similarly, the MVCI values in Crop-CASMA are rescaled to be represented in 8-bit integer in the range of [0,250]. The following formula is used for rescaling MVCI values in Crop-CASMA.
MVCI= 0,if (mm=-125)
mm+125,if (-125<mm<125)
250,if (mm=125)
For better visualization and to save space, the value range are truncated to fit in [0, 250]. Correspondingly, the map values for visualization are in [-100%, 100%] although the actual range can go beyond these limits.
MVC -- Maximum-Value Composite Procedure
A maximum-value composite procedure (or MVC) is a procedure used in compositing a series of multi-temporal geo-referenced NDVI images into a single NDVI image. This procedure compares all NDVI values on a pixel-by-pixel basis and retains only the highest value for each pixel location. This procedure will ran over all pixels and the output result is a MVC NDVI image.