Normalized Differential Vegetation Index (NDVI)

Normalized Differential Vegetation Index (NDVI) is one of the most widely used vegetation indices with applications in ecology, forestry, agriculture, wildlife and other disciplines. The NDVI dataset is based on the Moderate Resolution Imaging Spectroradiometer (MODIS) data. All raster files found in the viewer are based on the methods to fit double logistic curves to NDVI time series in Bischof et al. 2012. The only departures from Bischof et al.'s methods are: (1) we used 8-day NDVI composite instead of 16-day; and (2) we used snow cover data for each pixel to extend the "winter" period (i.e., floored NDVI values) until there is no snow cover for 2 consecutive weeks.

Variable	Metric	Units	Temporal availability	Description	Layers
DLC Parameters	dlc	various	Annual	Fitted parameter values (and standard errors) of the double logistic regression curve for each pixel. 8 layers per year: xmidS, scalS, xmidA, scalA, xmidS_SD, scalS_SD, xmidA_SD, scalA_SD. Value ranges: xmidS = 75–228; scalS = 1–20; xmidA = 167–288; scalA = 1–35.	Download Selected

Variable	Metric	Units	Temporal availability	Description	Layers
Cleaned NDVI Values	cleanVals	scaled 0–1	8-day	Cleaned 8-day NDVI values. Cleaning includes: flooring during winter, NA snow days after winter ends, running median filter, and scaling between 0 and 1.	Download Selected
Fitted Values	fittedVals	scaled 0–1	Daily (365 layers/year)	Fitted values from the double logistic curve on a daily basis for the entire year, scaled between 0 and 1 across all years combined. Note: no longer stored due to dataset size — extrapolate from dlcparams.
Instantaneous Rate of Green-up	IRGVals	scaled 0–1	Daily (365 layers/year)	First derivative of the scaled fitted values representing the Instantaneous Rate of Green-up (IRG) for the spring period only. Note: no longer stored due to dataset size — extrapolate from dlcparams.
Cumulative IRG	sumIRG	positive values	Daily (365 layers/year)	Cumulative summation of IRG values for each pixel on a daily basis across the entire year. Note: no longer stored due to dataset size — extrapolate from dlcparams.
Second Derivative of DLC	deriv2	scaled 0–1	Daily (365 layers/year)	Second derivative of the fitted double logistic curve for the spring period, calculated from scaled IRG values. Note: no longer stored due to dataset size — extrapolate from dlcparams.
Maximum IRG Value	maxIRG	scaled NDVI/day	Annual	Value of the maximum Instantaneous Rate of Green-up. Units are change in scaled NDVI per day. Each layer represents one year.
Spring Scale Parameter	scalS	—	Annual	Fitted spring scale parameter of the double logistic curve. Relates to maxIRG. Each layer represents one year.
Spring Midpoint Standard Error	xmidS_SD	days	Annual	Standard error of the fitted spring midpoint parameter (Julian day of peak rate of NDVI increase) of the double logistic curve. Each layer represents one year.
Date of Maximum IRG	maxIRGdate	Julian day	Annual	Julian date on which the maximum Instantaneous Rate of Green-up occurs. Each layer represents one year.
Date of Maximum NDVI	maxNDVIdate	Julian day	Annual	Julian date on which the maximum NDVI value occurs. Each layer represents one year.
Spring Start Date	springStart	Julian day	Annual	Julian date that spring begins, defined as the 1st second derivative of the NDVI curve. Each layer represents one year.
Spring End Date	springEnd	Julian day	Annual	Julian date that spring ends, defined as the 2nd second derivative of the NDVI curve. Each layer represents one year.
NDVI Scaling Quantiles	Lquantile / Uquantile	NDVI	Single layer	Lower (0.025) and upper (0.975) quantile values of the 14-year NDVI time series for each pixel, used to scale the time series between 0 and 1 for double logistic curve fitting.
Integrated Annual NDVI	csumNDVImax	NDVI	Annual	Total summation of csumNDVI (integrated NDVI) for each year. Each layer represents one year.

Remotely Sensed Phenology Measurements (RSPM)

RSPM provides annual vegetation phenology metrics from two data sources: eMODIS and eVIIRS. eMODIS collected data at 250 m resolution from 2001 to 2020; eVIIRS (375 m resolution) succeeded eMODIS from 2021 to present. To simplify data access, eMODIS has been resampled to 375 m resolution and data are processed from 2016 to present. Data is pulled from DEVISE. For complete details on data sources, processing, and metadata, please see the RSPM documentation.

Daily and monthly temporal intervals are unavailable for all RSPM variables.

Variable	Metric	Units	Scale factor	Temporal availability	Description	Source	Layers
Start Day of Photosynthesis	sost	day of year	× 1	Annual	Day of year on which measurable photosynthetic activity began in the vegetation canopy.	DEVISE	Download Selected
Day of Max. Photosynthesis	maxt	day of year	× 1	Annual	Day of year on which maximum photosynthetic activity occurred in the canopy.	DEVISE	Download Selected
End Day of Photosynthesis	eost	day of year	× 1	Annual	Day of year on which photosynthetic activity ceased in the vegetation canopy.	DEVISE	Download Selected
Days of Photosynthetic Activity	dur	days	× 1	Annual	Number of days photosynthetic activity was detected, describing the length of the growing season.	DEVISE	Download Selected
Time Integrated NDVI	tin	NDVI	× 0.01	Annual	Canopy photosynthetic activity across the entire growing season measured as NDVI above baseline (interpolated NDVI). A metric of cumulative photosynthetic activity for the year.	DEVISE	Download Selected