Airborne multiwavelength High Spectral Resolution Lidar (HSRL-2) observations during TCAP 2012 : Vertical profiles of optical and microphysical properties of a smoke/urban haze plume over the northeastern coast of the US

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License.We present measurements acquired by the world's first airborne 3 backscatter (β) + 2 extinction (α) High Spectral Resolution Lidar (HSRL-2). HSRL-2 measures particle backscatter coefficients at 355, 532, and 1064 nm, and particle extinction coefficients at 355 and 532 nm. The instrument has been developed by the NASA Langley Research Center. The instrument was operated during Phase 1 of the Department of Energy (DOE) Two-Column Aerosol Project (TCAP) in July 2012. We observed pollution outflow from the northeastern coast of the US out over the western Atlantic Ocean. Lidar ratios were 50-60 sr at 355 nm and 60-70 sr at 532 nm. Extinction-related Ångström exponents were on average 1.2-1.7, indicating comparably small particles. Our novel automated, unsupervised data inversion algorithm retrieved particle effective radii of approximately 0.2 μm, which is in agreement with the large Ångström exponents. We find good agreement with particle size parameters obtained from coincident in situ measurements carried out with the DOE Gulfstream-1 aircraft.Peer reviewedFinal Published versio

Mercury concentrations in two “great waters”

Although many sources of Hg to surface waters have been identified including atmospheric deposition, resuspension of contaminated sediments, and direct discharges, there are very few recent data on ambient concentrations in the large lakes. Thus, an investigation of Hg concentrations in Lake Champlain and Lake Michigan was completed in the summer of 1993. Three depths of water including the microlayer, 30 cm below the surface, and 1 m below the thermocline were collected for each sampling event using ultra-clean techniques. All samples were processed in the field for dissolved and particulate fractions in a portable plastic enclosure equipped with a HEPA filter, and then analyzed by dual amalgamation and cold vapor atomic fluorescence spectroscopy in a Class 100 clean room at the University of Michigan. In addition, samples were analyzed for other trace metals by ICP-MS. Results from the two field investigations include the following: (1) On average, Lake Michigan water samples had higher concentrations of Hg than Lake Champlain; (2) There was no consistent pattern of Hg concentrations in the water column; (3) There was variability in the concentrations of Hg from the same depths over consecutive sampling periods. This paper discusses these results, and examines the relationship between the patterns in mercury concentrations and other physical and chemical data collected during the investigation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43914/1/11270_2005_Article_BF01189709.pd

Radiometric calibration of a non-imaging airborne spectrometer to measure the Greenland ice sheet surface

Methods to radiometrically calibrate a non-imaging airborne visible-to-shortwave infrared (VSWIR) spectrometer to measure the Greenland ice sheet surface are presented. Airborne VSWIR measurement performance for bright Greenland ice and dark bare rock/soil targets is compared against the MODerate resolution atmospheric TRANsmission (MODTRAN®) radiative transfer code (version 6.0), and a coincident Landsat 8 Operational Land Imager (OLI) acquisition on 29 July 2015 during an in-flight radiometric calibration experiment. Airborne remote sensing flights were carried out in northwestern Greenland in preparation for the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) laser altimeter mission. A total of nine science flights were conducted over the Greenland ice sheet, sea ice, and open-ocean water. The campaign's primary purpose was to correlate green laser pulse penetration into snow and ice with spectroscopic-derived surface properties. An experimental airborne instrument configuration that included a nadir-viewing (looking downward at the surface) non-imaging Analytical Spectral Devices (ASD) Inc. spectrometer that measured upwelling VSWIR (0.35 to 2.5&thinsp;µm) spectral radiance (Wm-2sr-1µm-1) in the two-color Slope Imaging Multi-polarization Photon-Counting Lidar's (SIMPL) ground instantaneous field of view, and a zenith-viewing (looking upward at the sky) ASD spectrometer that measured VSWIR spectral irradiance (W&thinsp;m−2&thinsp;nm−1) was flown. National Institute of Standards and Technology (NIST) traceable radiometric calibration procedures for laboratory, in-flight, and field environments are described in detail to achieve a targeted VSWIR measurement requirement of within 5&thinsp;% to support calibration/validation efforts and remote sensing algorithm development. Our MODTRAN predictions for the 29 July flight line over dark and bright targets indicate that the airborne nadir-viewing spectrometer spectral radiance measurement uncertainty was between 0.6&thinsp;% and 4.7&thinsp;% for VSWIR wavelengths (0.4 to 2.0&thinsp;µm) with atmospheric transmittance greater than 80&thinsp;%. MODTRAN predictions for Landsat 8 OLI relative spectral response functions suggest that OLI is measuring 6&thinsp;% to 16&thinsp;% more top-of-atmosphere (TOA) spectral radiance from the Greenland ice sheet surface than was predicted using apparent reflectance spectra from the nadir-viewing spectrometer. While more investigation is required to convert airborne VSWIR spectral radiance into atmospherically corrected airborne surface reflectance, it is expected that airborne science flight data products will contribute to spectroscopic determination of Greenland ice sheet surface optical properties to improve understanding of their potential influence on ICESat-2 measurements.</p