@article {KNZ001531,
	title = {Comparing surface and mid-tropospheric CO2 concentrations from central U.S. grasslands},
	journal = {entropy},
	volume = {15},
	year = {2013},
	pages = {606 -623},
	abstract = {<p>Comparisons of eddy covariance (EC) tower measurements of CO2 concentration with mid-tropospheric observations from the Atmospheric Infrared Sounder (AIRS) allow for evaluation of the rising global signal of this greenhouse gas in relation to surface carbon dynamics. Using an information theory approach combining relative entropy and wavelet multi-resolution analysis, this study has explored correlations and divergences between mid-tropospheric and surface CO2 concentrations in grasslands of northeastern Kansas. Results show that surface CO2 measurements at the Kansas Field Station (KFS) and the Konza Prairie Biological Stations 1B (KZU) and 4B (K4B) with different land-cover types correlate well with mid-tropospheric CO2 in this region at the 512-day timescale between 2007 and 2010. Relative entropy further reveals that AIRS observations are indicative of surface CO2 concentrations for all land-cover types on monthly (32-day) and longer timescales. AIRS observations are also similar to CO2 concentrations at shorter timescales at sites KFS and K4B experiencing woody encroachment, though these results require further investigation. Differences in species composition and microclimate add to the variability of surface concentrations compared with mid-tropospheric observations.</p>},
	keywords = {LTER-KNZ, Atmospheric Infrared Sounder, Eddy covariance, information theory, Konza Prairie, relative entropy, wavelets},
	doi = {10.3390/e15020606},
	url = {https://www.mdpi.com/1099-4300/15/2/606},
	author = {Cochran, F.V. and N. Brunsell and Mechem, D.B.}
}
@article {KNZ001741,
	title = {Temporal scales of tropospheric CO2, precipitation, and ecosystem responses in the central Great Plains},
	journal = {Remote Sensing of Environment},
	volume = {127},
	year = {2012},
	pages = {316 - 328},
	abstract = {<p>Natural and anthropogenic sources of CO2 around the globe contribute to mid-tropospheric concentrations, yet it remains unknown how measurements of mid-tropospheric CO2 relate to regional ecosystem dynamics. NASA Atmospheric Infrared Sounder (AIRS) measurements of CO2 concentrations in the mid-troposphere from 2002 to 2010 were examined in relation to precipitation and vegetation phenology across the US Great Plains. Wavelet multi-resolution analysis and the information theory metric of relative entropy were applied to assess regional relationships between mid-tropospheric CO2, Normalized Difference Vegetation Index (NDVI), and precipitation (PPT). Results show that AIRS observations of mid-tropospheric CO2 exchange greater amounts of information with regional PPT and NDVI at seasonal, annual, and longer time scales compared to shorter time scales. PPT and NDVI contribute to mid-tropospheric CO2 at the 18-month time scale, while spatial patterns seen at this time scale for PPT and mid-tropospheric CO2 are reflective of the influence of PPT on NDVI at the annual scale. Identification of these dominant temporal scales may facilitate utilization of AIRS CO2 for monitoring regional source/sink dynamics related to climate and land-use/cover change.</p>},
	keywords = {LTER-KNZ, Atmospheric Infrared Sounder, Land{\textendash}atmosphere interactions, relative entropy, wavelets},
	issn = {00344257},
	doi = {10.1016/j.rse.2012.09.012},
	url = {https://www.sciencedirect.com/science/article/abs/pii/S0034425712003665?via\%3Dihub},
	author = {Cochran, F.V. and N. Brunsell}
}
