Annual NDVI Change Defoliation Watch

Track paired annual NIR/red NDVI drops against caller screening threshold, retaining greening; unlike SWIR-based dNBR, input bands differ and neither index diagnoses defoliation agents.

Description

NDVI uses near-infrared and red bands to describe a vegetation signal.

NDVI uses near-infrared and red bands to describe a vegetation signal. A pre-minus-post drop can be negative when the observed signal increases.^[1]

Track paired annual NIR/red NDVI drops against caller screening threshold, retaining greening; unlike SWIR-based dNBR, input bands differ and neither index diagnoses defoliation agents.

When to use Annual NDVI Change Defoliation Watch

Use this tool to track paired annual NIR/red NDVI drops against caller screening threshold, retaining greening; unlike SWIR-based dNBR, input bands differ and neither index diagnoses defoliation agents.

Gather the tree inventory, plot measurements or model parameters. Check diameter, area, time and moisture conventions; keep paired observations aligned.

How to use Annual NDVI Change Defoliation Watch and understand its results

Gather the tree inventory, plot measurements or model parameters. Check diameter, area, time and moisture conventions; keep paired observations aligned.
Enter preYearNir, preYearRed, postYearNir, postYearRed, callerMinimumNdviDrop using the field table and calculation rules, then run the tool.
Read preYearNdvi, postYearNdvi, signedNdviDrops, aboveCallerDropFlags. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
preYearNir	Pre year nir	list of number	Required
preYearRed	Pre year red	list of number	Required
postYearNir	Post year nir	list of number	Required
postYearRed	Post year red	list of number	Required
callerMinimumNdviDrop	Caller minimum ndvi drop	number	Required

Pair four nonnegative measured-band lists with positive NIR+red sums and a nonnegative screening threshold. Return pre/post indices, signed drops and flags only for strict threshold exceedance.

Paired lists must be nonempty and have equal lengths.

NDVI=(NIR−red)/(NIR+red); drop=pre-year NDVI−post-year NDVI

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
preYearNdvi	Pre year ndvi	list of number
postYearNdvi	Post year ndvi	list of number
signedNdviDrops	Signed ndvi drops	list of number
aboveCallerDropFlags	Above caller drop flags	list of number

json

{
  "input": {
    "preYearNir": [
      0.8,
      0.6
    ],
    "preYearRed": [
      0.2,
      0.4
    ],
    "postYearNir": [
      0.6,
      0.8
    ],
    "postYearRed": [
      0.4,
      0.2
    ],
    "callerMinimumNdviDrop": 0.2
  },
  "output": {
    "preYearNdvi": [
      0.6000000000000001,
      0.19999999999999996
    ],
    "postYearNdvi": [
      0.19999999999999996,
      0.6000000000000001
    ],
    "signedNdviDrops": [
      0.40000000000000013,
      -0.40000000000000013
    ],
    "aboveCallerDropFlags": [
      1,
      0
    ]
  }
}

Limitations and assumptions

Sensor comparability and atmospheric correction are supplied. A drop does not diagnose a defoliation agent; NBR uses different bands.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use dNBR Burn Severity Delta NDVI: Compute paired NIR/SWIR normalized burn ratio and signed pre-minus-post dNBR; title’s NDVI wording is not used because NBR requires SWIR, and severity class/local ecological outcome is not inferred. For a complementary task, use Current-Year Foliage Retention Percent: Audit independently established current-year needle inventory with observability bounds; older needle cohorts are not pooled and retention alone does not identify stress/disease.

References

Annual NDVI Change Defoliation Watch — tool.io

Similar or alternative tools

dNBR Burn Severity Delta NDVI
Compute paired NIR/SWIR normalized burn ratio and signed pre-minus-post dNBR; title’s NDVI wording is not used because NBR requires SWIR, and severity class/local ecological outcome is not inferred.
Current-Year Foliage Retention Percent
Audit independently established current-year needle inventory with observability bounds; older needle cohorts are not pooled and retention alone does not identify stress/disease.