How the metrics are defined?
We analysed the NDVI dynamics curve to extract the 13 phenologic metrics. These metrics represent the seasonal growth conditions of the crop. Derivation of metrics from the NDVI dynamics curve should start by calculating the Onset and Offset metrics, as the rest of the metrics are defined on the basis of them.
OnsetV and OnsetT
We defined Onset as the time when the NDVI dynamics curve accelerates consistently in the early stage of the growth period.Onset is defined at which the curve shows consecutive increase and gains at least the user defined threshold value. The threshold is used to avoid high NDVI values which may be caused by weed growth prior to the crop growth season. It is defined as the user provided percentage value above the minimum NDVI values in the early growth season (Before Maximum NDVI), which is assuming the weed clearance around three to two weeks before sowing.
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OffsetV and OffsetT
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Offset is defined as the point in time where the NDVI dynamics curve finishes its deceleration. The offset is defined as the point where the NDVI value falls below a the percentage of user defioned value below the minimum value after maximum NDVI, which is the time when the crop totally loses greenness before harvest.
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MaxV and MaxT
The value and time of maximum vegetation index of the growing season. At this stage full canopy coverage at the beginning of Anthesis/flowering when the anthers are green; Zadoks growth stage 60-69.
GreenUpSlope
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The GreenupSlope is calculated as the slope of the line connecting Onset and MaxNDVI. This metric measurement of how fast the crop undergoes the stages to reach to maximum greenness. This metric measures the ratio of increase in greenness over time before the maximum greenness attained, at anthesis. The pre anthesis time is when the crop ears are formed and grow (Poole and Hunt, 2014; Satorre and Slafer, 1999). Thus the steeper slope indicates short time to undergo this phases.
BrownDownSlope
BrownDownSlope is the slope of the line connecting the MaxNDVI and Offset. This metric measurement of how fast the crop passes through after anthesis growth stages. During these stages the sugar produces by photosynthesis are transported to fill the grain (Poole and Hunt, 2014). Thus the steeper BrownDownSlope indicates short time to undergo grain filling, which is one of the factor to determine the crop potential.
TINDVIbeforeMax
This metric is calculated as the NDVI sum between Onset and MaxNDVI. This metric indicates the pre-anthesis crop growth. Stress during the Pre-anthesis period affects the number of grains per head and the potential grain size, results in reduction of yield potential (Poole and Hunt, 2014). The pre-anthesis growth is also important for reducing evaporation from the soil surface. Pre-anthesis growth contribute directly to yield through the storage of the sugar produced by photosynthesis, which accumulate in the stem and translocated to the grain after anthesis. Crops that have produced large dry matter before anthesis could have large yield potential, however they will also have a risk of not being able to fill the grain due to high evapotranspiration form large leaf area.
TINDVIAterMax
TINDVIAfterMax is defined as the sum of NDVI values between MaxNDVI and Offset. This metric indicates the post anthesis growth. During post-anthesis the growth products are transported in to the grain. At this stage water is used efficiently to transport the growth products to the grain; limited water supply during this growth period highly affect the yield potential. Large canopy crops might face difficulty to fill the grain due to water loss through evapotranspiration (Poole and Hunt, 2014).
TINDVI
TINDVI is the sum of TINDVIBeforeMax and TINDVIAfterMax. A measure of the biomass productivity of the growing season (Calera et al., 2004; Hill and Donald, 2003). High biomass productivity is associated with high final yield (Labus et al., 2002).
Asymmetry
is calculated as the diference between TINDVIBeforeMax and TINDVIAfterMax. This metric measures the relative crop canopy size during before and after anthesis of the crop growth. Generally, size and duration of crop canopy is controlled mainly by soil water availability (GRDC, 2005). If the canopy duration in the grain filling stage is high value indicates large crop canopy development before anthesis, which might be interpreted as high yield potential. On the other hand, extensive canopy size before anthesis during formation of ears might indicate high yield potential, however the large amount of leaf area could use water quick and rapidly exhaust the supply result a decline in yield potential (Poole and Hunt, 2014). Thus optimal canopy size and duration is the main aim of canopy management practices, particularly to maintain the canopy during the grain filling season (Poole and Hunt, 2014).
LengthGS-
The length of Growing season is defined as the time elapsed from Onset to Offset. The duration of time the crop takes to go through the all stages of crop growth.
BeforeMaxT-
The length of time elapsed from Onset to Maximum. This metric can theoretically relate with the duration of time the crop takes to go through the early growth stages of crop growth, before anthesis.
AfterMaxT-
The length of time elapsed from Maximum NDVI to Offset. This metric can theoretically relate with the duration of time the crop takes to go through the late growth stages of crop growth, after anthesis.
