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Title: Using data from Landsat, MODIS, VIIRS and PhenoCams to monitor the phenology of California oak/grass savanna and open grassland across spatial scales

tThe Mediterranean-type oak/grass savanna of California is composed of widely spaced oak trees withunderstory grasses. These savanna regions are interspersed with large areas of more open grasslands.The ability of remotely sensed data (with various spatial resolutions) to monitor the phenology in thesewater-limited oak/grass savannas and open grasslands is explored over the 2012–2015 timeframe usingdata from Landsat (30 m), the MODerate resolution Imaging Spectroradiometer (MODIS – gridded 500 m),and the Visible Infrared Imaging Radiometer Suite (VIIRS – gridded 500 m) data. Vegetation phenologydetected from near-ground level, webcam based PhenoCam imagery from two sites in the Ameriflux Net-work (long-term flux measurement network of the Americas) (Tonzi Ranch and Vaira Ranch) is upscaled,using a National Agriculture Imagery Program (NAIP) aerial image (1 m), to evaluate the detection ofvegetation phenology of these savannas and grasslands with the satellite data. Results show that the Nor-malized Difference Vegetation Index (NDVI) time series observed from the satellite sensors are all stronglycorrelated with the PhenoCam NDVI values from Tonzi Ranch (R2> 0.67) and Vaira Ranch (R2> 0.81). How-ever, the different viewing geometries and spatial coverage of the PhenoCams and the various satellitesensors may cause differences in the absolute phenological transition dates. Analysis of frequency his-tograms of phenological datesmore » illustrate that the phenological dates in the relatively homogeneous opengrasslands are consistent across the different spatial resolutions, in contrast, the relatively heterogeneousoak/grass savannas display has somewhat later greenup, maturity, and dormancy dates at 30 m resolu-tion than at 500 m scale due to the different phenological cycles exhibited by the overstory trees and theunderstory grasses. In addition, phenologies derived from the MODIS view angle corrected reflectance(Nadir BRDF-Adjusted Reflectance – NBAR) and the newly developed VIIRS NBAR are shown to providecomparable phenological dates (majority absolute bias ≤2 days) in this area.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [6] ;  [7] ;  [7] ;  [7] ;  [1]
  1. Univ. of Massachusetts, Boston, MA (United States)
  2. Univ. of North Dakota, Grand Forks, ND (United States)
  3. South Dakota State Univ., Brookings, SD (United States)
  4. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
  5. Harvard Univ., Cambridge, MA (United States)
  6. Enironmental Protection Agency of Aosta Valley, Aosta (Italy)
  7. Univ. of California, Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
SC0016011
Type:
Published Article
Journal Name:
Agricultural and Forest Meteorology
Additional Journal Information:
Journal Volume: 237-238; Journal Issue: C; Journal ID: ISSN 0168-1923
Publisher:
Elsevier
Research Org:
Univ. of Massachusetts, Boston, MA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Savannas; Land surface phenology; near surface webcams; Satellite sensor resolution; MODIS; VIIRS; Landsat
OSTI Identifier:
1392711
Alternate Identifier(s):
OSTI ID: 1426772