Aircraft‐Based Flux Sampling Strategies

Abstract

One of the essential elements of plant growth is carbon dioxide assimilation and water vapor loss. Measuring the exchange of these gases can provide an accurate picture of plant growth, health, and ultimate yield. This report describes the instrumentation used on the Canadian flux aircraft and the type of data collected for measuring gas exchange over large areas. It presents flux measurements of carbon dioxide, sensible heat (H) and latent heat (LE) using the eddy‐covariance technique. This technique provides the most direct measurements of mass and energy exchange at the land–atmosphere interface. Flux measurements obtained over wetlands near James Bay, the boreal forest in northern Saskatchewan, grasslands in Kansas, agricultural crops in California, and over the city of Fresno in California are presented as examples of the potential of this technique to characterize transfer processes over complex ecosystems. The accuracy of aircraft‐based flux measurements is examined using data obtained with other aircraft during wing‐to‐wing formation flights and with several tower‐based systems during tower fly‐by. Finally, examples of the use of these data for interpreting satellite data and for characterizing the photosynthetic response of a wide range of vegetation are presented.

Creating Surface Flux Maps from Airborne Measurements: Application to the Mackenzie Area GEWEX Study MAGS 1999

“…One of our grid runs, which is the basis for the wavelet flux calculation, is only between 15 and 16 km long, which is probably often not sufficient to capture all longwave flux contributions. Therefore, we used another flight pattern, called a regional run (Desjardins et al 2000) to quantify the flux for the entire spectral range. The MAGS regional run was 100 km long, and was located approximately 60 km south of the grid, between coordinates 68 • 08.0 N, 133 • 15.0 W and 67 • 15.0 N, 133 • 50.0 W. Regional runs were flown within a few days of the grid flight, sometimes even on the same day, so that we assume that the spectrum of atmospheric transport was similar to the grid flight shortly before or afterwards.…”

Flux Footprints in the Convective Boundary Layer: Large-Eddy Simulation and Lagrangian Stochastic Modelling

“…Typically, the footprint has been used to characterize the applicability of near-surface measurements. However, high towerand aircraft-based measurements which are now commonly used (Desjardins et al 2000(Desjardins et al , 2010 bring the receptor to the lower or middle levels of the atmospheric boundary layer. For example, the measurement track of an instrument carried by an aircraft may span 10-100 km horizontally, with a wide range of measurement heights (Mauder et al 2007).…”

Flux measurements by the NRC Twin Otter atmospheric research aircraft: 1987–2011

“…Such transfer can best be quantified using aircraft-based measurements. The versatility of aircraft-based flux measurements was demonstrated by showing the change in the O 3 concentration and flux upwind and downwind of a major highway (Guo et al, 1995) and by showing the magnitude of the CO 2 concentration and flux at an altitude of 150 m above the city of Fresno (Desjardins et al, 2000).…”

“…N 2 O, CH 4 ), were measured using the Relaxed Eddy Accumulation (REA) technique (Pattey et al, 2006). Details on the aircraft, the instrumentation and various sampling strategies are presented in Desjardins et al (2000).…”

“…1) has been instrumented to accurately measure the three components of atmospheric motion and the vertical fluxes of heat, momentum, water vapour, carbon dioxide (CO 2 ), ozone (O 3 ), methane (CH 4 ) and nitrous oxide (N 2 O), as well as other supporting meteorological and spectral data (Desjardins and MacPherson, 1991;Desjardins et al, 2000). Since one of the aircraft's primary research roles is in the field of land/atmosphere interactions, a number of remote sensing instruments were used to document surface conditions during flux-measuring campaigns.…”