Understanding Northern Latitude Vegetation Greening and Browning Proceedings of a Workshop (2019) / Chapter Skim
Currently Skimming:
Methods Used to Evaluate Change and Detect Trends
Methods Used to Evaluate Change and Detect Trends
Pages 21-28
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 21... ...
AVHRR provides information at an 8-km resolution and provides usable data from 1982 to present. Christopher Neigh, NASA Goddard Space Flight Center, discussed uncertainties associated with remote sensing platforms and NDVI estimates, focusing primarily on this satellite platform.
|
From page 22... ...
AVHRR GAC are the most commonly used data to study greening and browning trends. Concerns exist that some of the approaches used to correct the data can reduce sensitivity of NDVI change hotspots.
|
From page 23... ...
A challenge with using NDVI data across these sensors is that careful cross-calibration is necessary to avoid artificial positive trends that can emerge by simply combining estimates. The Landsat record covers much of the same time period as AVHRR, and comparison of greening and browning trends between the two platforms was discussed throughout the workshop as a key example of the challenge in reconciling observations across methodological approaches.
|
From page 24... ...
NEW REMOTE SENSING TECHNOLOGIES TO STUDY GREENING AND BROWNING In addition to the long records available from a number of remote sensing instruments, there are also new campaigns and technologies being adopted to evaluate greening and browning trends. These approaches can provide new types of data and can also serve to bridge gaps in spatial scales that exist among more traditional methodologies.
|
From page 25... ...
Solar-Induced Fluorescence SIF can provide information on greening and browning because it is viewed as a proxy for GPP that captures its spatial and temporal resolution, explained Xi Yang, University of Virginia. SIF data have been shown to correlate well with other GPP products at the global scale, and hotspots of fluorescence can be detected in high productivity regions including the tropics and the U.S.
|
From page 26... ...
is of particular interest to the SIF community because it currently provides the highest temporal and spatial resolution data, beginning in 2018, and has the highest resolution. Lidar, Hyperspectral, and Thermal Airborne Imager Doug Morton, NASA Goddard Space Flight Center, stressed that airborne campaigns provide unique access to remote areas and allow for coincident, high-resolution measurements of numerous metrics that can inform understanding of vegetation change.
|
From page 27... ...
Deploying drones may also be a pathway to expand remote sensing coverage in remote regions to provide context for field measurements of vegetation in the absence of routine airborne campaigns, Morton explained. Meddens indicated that high-resolution drone imagery could allow for detection of tree-level mortality occurring with insect outbreaks that are currently undetectable at fine scale with satellite observations.
|
From page 28... ...
The difference between the measured NEE and the modeled respiration provides an estimate of GPP. In the absence of darkness during the summer months at high latitudes, respiration can be estimated over a number of days using light response curves and these measurements are then related to background soil temperature or air temperature.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.