High-resolution Airborne Measurements Research Articles

Arctic Sea Ice Characterization Using Spaceborne Fully Polarimetric L-, C-, and X-Band SAR With Validation by Airborne Measurements

In recent years, spaceborne synthetic aperture radar (SAR) polarimetry has become a valuable tool for sea ice analysis. Here, we employ an automatic sea ice classification algorithm on two sets of spatially and temporally near coincident fully polarimetric acquisitions from the ALOS-2, Radarsat-2, and TerraSAR-X/TanDEM-X satellites. Overlapping coincident sea ice freeboard measurements from airborne laser scanner data are used to validate the classification results. The automated sea ice classification algorithm consists of two steps. In the first step, we perform a polarimetric feature extraction procedure. Next, the resulting feature vectors are ingested into a trained neural network classifier to arrive at a pixelwise supervised classification. Coherency matrix-based features that require an eigendecomposition are found to be either of low relevance or redundant to other covariance matrix-based features, which makes coherency matrix-based features dispensable for the purpose of sea ice classification. Among the most useful features for classification are matrix invariant-based features (geometric intensity, scattering diversity, and surface scattering fraction). Classification results show that 100% of the open water is separated from the surrounding sea ice and that the sea ice classes have at least 96.9% accuracy. This analysis reveals analogous results for both X-band and C-band frequencies and slightly different for the L-band. The subsequent classification produces similarly promising results for all four acquisitions. In particular, the overlapping image portions exhibit a reasonable congruence of detected sea ice when compared with high-resolution airborne measurements.

Sargassum coverage in the northeastern Gulf of Mexico during 2010 from Landsat and airborne observations: Implications for the Deepwater Horizon oil spill impact assessment

Using high-resolution airborne measurements and more synoptic coverage of Landsat measurements, we estimated the total Sargassum coverage in the northeastern Gulf of Mexico (NE GOM) during 2010, with the ultimate purpose to infer how much Sargassum might have been in contact with oil from the Deepwater Horizon oil spill. Mean Sargassum coverage during the four quarters of 2010 for the study region was estimated to range from ~3148±2355km2 during January–March to ~7584±2532km2 during July–September (95% confidence intervals) while estimated Sargassum coverage within the integrated oil footprint ranged from 1296±453km2 (for areas with >5% thick oil) to 736±257km2 (for areas with >10% thick oil). Similar to previous studies on estimating Sargassum coverage, a direct validation of such estimates is impossible given the heterogeneity and scarcity of Sargassum occurrence. Nonetheless, these estimates provide preliminary information to understand relative Sargassum abundance in the NE GOM.

A Comparison of Airborne Microwave Brightness Temperatures and Snowpack Properties Across the Boreal Forests of Finland and Western Canada

The seasonal snowpack across the boreal forest is an important national resource in both Canada and Finland, contributing freshwater for agriculture, human consumption, and hydropower generation. In both countries, satellite passive microwave data are utilized to provide operational information on snow depth and snow water equivalent (SWE) throughout the snow cover season. Airborne passive microwave surveys conducted independently across Finland and western Canada during March and April 2005 and March 2006 provided the opportunity to assess the level of similarity in snowpack physical properties and brightness temperature response to snowpack qualities using two independent data sets. The primary objectives of these campaigns were to determine the influence of small-scale heterogeneity on satellite data, using relatively high resolution airborne measurements, and to assess the Helsinki University of Technology (HUT) snow emission model capability of predicting emitted brightness temperatures under varying snowpack and landscape conditions. Comparisons of brightness temperature emissions over different land cover types showed a clear distinction of wetlands and snow-covered ice from forested and open areas. This is reflected also as a strong relationship between 6.9-GHz measurements and fractional lake cover in both Canada and Finland, with relationships at 18 and 37 GHz being less consistent between data sets. Comparisons of experimental data versus HUT snow emission model predictions showed relatively good agreement between the simulations and airborne data, specifically for the Finnish data set.

Aircraft measurements of aerosol black carbon from a coastal location in the north-east part of peninsular India during ICARB

During the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) over India, high-resolution airborne measurements of the altitude profiles of the mass concentrations (MB) of aerosol black carbon (BC) were made off Bhubaneswar (BBR, 85.82°E, 20.25°N), over northwest Bay of Bengal, in the altitude region upto 3 km. Such high-resolution measurements of altitude profiles of aerosols are done for the first time over India. The profiles showed a near-steady vertical distribution of MB modulated with two small peaks, one at 800m and the other at ∼2000m. High resolution GPS (Global Positioning System) sonde (Vaisala) measurements around the same region onboard the research vessel Sagar Kanya (around the same time of the aircraft sortie) revealed two convectively well mixed layers, one from ground to ∼700m with an inversion at the top and the other extends from 1200m to ∼2000m with a second inversion at ∼2200m and a convectively stable region in the altitude range 700–1200m. The observed peaks in the MB profile are found to be associated with these temperature inversions. In addition, long-range transport from the Indo-Gangetic Plain (IGP) and deserts lying further to the west also influence the vertical profile of BC. Latitudinal variation of MB showed a remarkable land ocean contrast at the 500m altitude (within the well mixed region) with remarkably lower values over oceans, suggesting the impact of strong sources over the mainland. However, above the ABL (at 1500m), the latitudinal variations were quite weak, and this appears to be resulting from the impact of long-range transport. Comparison of the altitude profiles of MB over BoB off BBR with those obtained during the earlier occasion over the inland stations of Hyderabad and Kanpur showed similarities above ∼500m, with MB remaining around a steady value of ∼1 μg m−3. However, large differences are seen within the ABL. Even though the observed MB values are not unusually high, their near constancy in the vertical column will have important implications to radiative forcing.

Transport of air pollutants from the boundary layer to the free tropospere over complex terrain

Transport of trace gases from the atmospheric boundary layer (ABL) to the free troposphere (FT) is negligible under cloudless conditions over uniform terrain. However, over complex topography, an instantaneous exchange between the structured and discontinuous ABL and the FT may be possible. Aircraft measurements at the ABL - FT transition zone reveal pollutant fluxes larger than could be expected from an one-way entrainment. Those fluxes significantly influence regional pollutant budgets. Above populated areas and under high insolation, flux of O 3 and NO 2 is usually directed from the ABL to the free troposphere, where the overall tropospheric ozone production is altered. The exchange with the free troposphere is examined for two mesoscale areas: The Swiss Plateau in Switzerland and the Hong Kong area in Asia. The Swiss Plateau exhibits mainly hilly terrain while the Hong Kong area displays a very complex terrain with sea surfaces as well as steep mountains. The flux across the top of the ABL is obtained from high resolution airborne measurements taken by the NCAR King Air. A flux partitioning is performed to identify the most important atmospheric scales contributing to this vertical transport. Turbulent transport is important for the Swiss Plateau as well as Hong Kong. Over Hong Kong, larger scales also contribute significantly to vertical exchange. This larger scale transport might indicate that local thermotopographic circulations are involved. A statistical model based upon the measurements over the Swiss Plateau allows a rough estimation of the vertical flux densities from the concentration, potential temperature and windshear profiles for cases where high resolution airborne measurements are not available.