IPY-246_05 - ABACUS - Aircraft Fluxes and Remote Sensing

The aircraft will be used in support of hypotheses 2, 3, 6 and 7. The system will produce area-averaged fluxes of CO2, CH4, water vapour and heat; it will also produce maps of the variability in the main drivers of land-atmosphere exchange such as albedo and surface roughness. Multiple passes on several consecutive days using the on-board spectroradiometer will be compared with composite MODIS scenes (from WP6) to scale up radiometric indices such as NDVI and PRI. Some of the passes will be made co-incident with IKONOS overpasses for similar purposes. The University of Edinburgh's recently purchased Dimona MPX aircraft is capable of low and slow flying, with wing pods, each capable of carrying up to 50 kg of scientific payload.

The aircraft can fly as low as 10 m above ground at air speeds as low as 25 m s-1. The aircraft has a combined inertial navigation system, multiple GPS sensors and radar altimeter for precise altitude and position information. The basic system includes a BAT probe (for precise wind speed measurements), a LI-7500 open-path IRGA (for CO2 and H2O fluxes), a LI-6262 (for atmospheric CO2 profiles). We will use the ASD Spectroradiometer from the NERC Field Spectroscopy Unit (for radiometric indices, in conjunction with WP6). The aircraft has an automated flask sampling system that we will use for sampling the atmospheric concentration of 14C and CH4 in vertical profiles above both sites. The aircraft will be flown in two main modes viz. in repeated transects across the landscape (typical flight legs of up to 20 km) and also in ''box'' patterns at altitudes from near the surface to the top of the planetary boundary layer. The transect flights will use both radiometric and flux sensors to establish the role of surface heterogeneity on measured fluxes at both tower and surface layer heights (Mahrt et al, 2001). Similar studies in the past have discovered that regional scale evaporation can be adequately estimated by such a methodology (Isaac et al 2004).

The number of passes required to reduce the error estimates partly depends on the scale of the surface heterogeneity but typically several passes are averaged to obtain representative flux estimates and this will be planned for taking into account the endurance of the aircraft. Box flight patterns have been flown in experiments such as FIFE to examine large scale budgets of heat and moisture and we shall derive the C budgets for the sites using this methodology. Laser altimetry will be used to assess snow depth by repeated sampling during the thaw.

Deliverables:
A. Error analysis of aircraft fluxes (with WP4, paper in Q.J. Roy. Met. Soc.).
B. A lagrangian transport model relating aircraft observations to surface fluxes (with WP7, paper in Bound.-Layer Met.).
C. An analysis of how surface fluxes of C and water and radiometric signatures vary across the landscape at Abisko.
D. A repeat of C. (A paper combining C & D, addressing H7 and H3c in Bound. Layer Met.);
E. Evaporative fraction and maximum stomatal conductance for mid-day periods at three times during each field season at Abisko, and snow cover estimates during Spring.
F. A repeat of E at Kevo. (A paper in Glob. Ch. Biol. based on E and F, addressing H3c).
G. An analysis of mobilisation of 14C upon snowmelt (with WP2, paper in Nature), addressing H3b.
H. Landscape scale fluxes of CO2 and CH4 at Abisko.
I. A repeat of H at Kevo. (A paper in Glob. Biogeo. Cyc. addressing H6).

Tasks:
1. Flight planning, installation of aircraft systems, pilot training and familiarisation; negotiation with Aviation authorities in Sweden, Norway and Finland.
2. Develop backward lagrangian dispersion model, and relate airborne fluxes of CO2 and CH4 to land surface sources.
3. Delivery of aircraft to Narvik (for Abisko flights) and Laksek (for Kevo flights) (May 2007, 2008).
4. Initial reconnaissance flights at Abisko and Kevo to confirm flight planning (early May 2007, 2008).
5. Analyse early transect flights to assess the number of passes for averaging purposes.
6. Aerial surveys of both sites using spectroradiometer and laser altimeter (throughout field seasons)
7. Aerial surveys of both sites using flux and turbulence sensors to look for dynamical heterogeneity in land-atmosphere interaction (throughout flight seasons).
8. ''Box-Budget'' flights at three times in both field seasons for CO2 and CH4 regional budgets.
9. Provide spectroradiometer data to WP6 (throughout both field seasons)
10. Operation of Boreal Laser CH4 instrument at both sites over both field seasons.