References, Definitions, Acronyms, and Abbreviations

Referenced Documents

1. Progress‐Terms and Definitions (2018). United States Department of Agriculture, National Agricultural Statistics Service. https://www.nass.usda.gov/Publications/National_Crop_Progress/Terms_and_Definitions/index.php#moisture, accessed on April 1, 2020.

2. SMAP Level-4 Data Products: https://gmao.gsfc.nasa.gov/GMAO_products/SMAP_L4/docs/, accessed on April 1, 2020.

3. Colliander, A., Yang, Z., Mueller, R., Sandborn, A., Reichle, R., Crow, W., et al. (2019). Consistency between NASS surveyed soil moisture conditions and SMAP soil moisture observations. Water Resources Research, 55. August 2019.https://doi.org/10.1029/2018WR024475.

4. Z. Yang, L. Di, G. Yu and Z. Chen, "Vegetation condition indices for crop vegetation condition monitoring," 2011 IEEE International Geoscience and Remote Sensing Symposium, Vancouver, BC, 2011, pp. 3534-3537. DOI: 10.1109/IGARSS.2011.6049984.

5. Z. Yang, G. Yu, L. Di, B. Zhang, W. Han and R. Mueller, "Web service-based vegetation condition monitoring system - VegScape,"2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, Melbourne, VIC, 2013, pp. 3638-3641.

6. Holben, Brent (1986). "Characteristics of maximum-value composite images from temporal AVHRR data". International Journal of Remote Sensing. 7 (11): 1417- 1434. Bibcode:1986IJRS....7.1417H. doi:10.1080/01431168608948945.

Definitions, Acronyms, and Abbreviations

Definitions

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:

$$SMA = \ \frac{SM - \text{SM}_{m}}{\text{SM}_{m}} \times 100\%$$

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:

$$NDVI = \ \frac{NIR - Red}{NIR + Red}$$

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:

$${NDVI = \ \frac{\text{Band}_{2} - \text{Band}_{1}}{\text{Band}_{2} + \text{Band}_{1}} \times 125 + 125}$$

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:

$$VCI = \ \frac{NDVI - \text{NDVI}_{\min}}{\text{NDVI}_{\max} + \text{NDVI}_{\min}} \times 250$$

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:

$$mm = \ \frac{NDVI - \text{NDVI}_{m}}{\text{NDVI}_{m}} \times 100$$

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.

$$MVCI = \ \left\{ \begin{matrix} 0, if\ (mm \leq - 125) \\ mm + 125, if\ ( - 125 < mm < 125) \\ 250, if\ (mm \geq 125) \\ \end{matrix} \right.\ $$

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.

Acronyms and Abbreviations

AOI -- Area of Interest

MODIS -- Moderate Resolution Imaging Spectroradiometer

CDL -- Cropland Data Layer

SMAP -- Soil Moisture Active Passive

NDVI -- Normalized Difference Vegetation Index

MVCI -- Mean Vegetation Condition Index

SM -- Soil Moisture

SMA -- Soil Moisture Anomaly

VCI - Vegetation Condition Index