We describe the development of a near-infrared laser heterodyne radiometer: the precision heterodyne oxygen-corrected spectrometer (PHOCS). The prototype instrument is equipped with two heterodyne receivers for oxygen and water (measured near 1278 nanometers) and carbon dioxide (near 1572 nanometers) concentration profiles, respectively. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1651 nanometers. Oxygen measurements are intended to provide dry gas corrections and—more importantly—determine accurate temperature and pressure profiles that, in turn, improve the precision of the C O 2 and H 2 O column retrievals. Vertical profiling is made feasible by interrogating the very low-noise absorption lines shapes collected at ≈ 0.0067 c m − 1 resolution. PHOCS complements the results from the Orbiting Carbon Observatory (OCO-2), Active Sensing of C O 2 Emissions over Nights, Days, and Seasons (ASCENDS), and ground-based Fourier transform spectrometers. In this paper, we describe the development of the instrument by Mesa Photonics and present the results of initial tests in the vicinity of  Washington, DC.

Nitrogen (N) and phosphorus (P) concentrations and N:P ratios critically influence periphyton productivity and nutrient cycling in aquatic ecosystems. In coastal wetlands, variations in hydrology and water source (fresh or marine) influence nutrient availability, but short-term effects of drying and rewetting and long-term effects of nutrient exposure on periphyton nutrient retention are uncertain. An outdoor microcosm experiment simulated short-term exposure to variation in drying-rewetting frequency on periphyton mat nutrient retention. A 13-year dataset from freshwater marshes of the Florida Everglades was examined for the effect of long-term proximity to different N and P sources on mat-forming periphyton nutrient standing stocks and stoichiometry. Field sites were selected from one drainage with shorter hydroperiod and higher connectivity to freshwater anthropogenic nutrient supplies (Taylor Slough/Panhandle, TS/Ph) and another drainage with longer hydroperiod and higher connectivity to marine nutrient supplies (Shark River Slough, SRS). Total P, but not total N, increased in periphyton mats exposed to both low and high drying-rewetting frequency with respect to the control mats in our experimental microcosm. In SRS, N:P ratios slightly decreased downstream due to marine nutrient supplies, while TS/Ph increased. Mats exposed to short-term drying-rewetting had higher nutrient retention, similar to nutrient standing stocks from long-term field data. Periphyton mat microbial communities may undergo community shifts upon drying-rewetting and chronic exposure to nutrient loads. Additional work on microbial species composition may further explain how periphyton communities interact with drying-rewetting dynamics to influence nutrient cycling and retention in wetlands.

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An analysis of historic pressure and temperature profiles from radiosonde launches for use as Bayesian priors in retrieval of mixing ratios for greenhouse gases (GHGs) from Laser Heterodyne Radiometry (LHR) spectra is reported.

<div>We present an analysis of historic pressure and temperature profiles from radiosonde</div><div>launches that will be used in retrieval of mixing fractions for greenhouse gases (GHGs, including</div><div>carbon dioxide, methane, and water vapor) in Laser Heterodyne Radiometry (LHR) data. With</div><div>over 2,700 stations worldwide, the global coverage for weather balloon observations is</div><div>extensive. Radiosonde stations included in the Integrated Global Radiosonde Archive (IGRA),</div><div>are launched simultaneously twice daily at 00:00 and 12:00 UTC. Global stations span all time</div><div>zones in both the Northern and Southern Hemisphere.</div><div> </div><div>Mesa Photonics and George Washington University are developing a variant of LHR</div><div>known as Precision Heterodyne, Oxygen-Corrected Spectroscopy (PHOCS) that simultaneously</div><div>collects high-resolution, oxygen spectral line shape data. Because oxygen concentrations in the</div><div>troposphere and lower stratosphere are constant, these line shapes are uniquely sensitive to both</div><div>temperature and pressure profiles and constrained fitting of these line shapes enables more</div><div>precise GHG concentration retrievals.</div><div> </div><div>Our approach is to collect historic data over several years (typically the prior decade) for</div><div>a particular date window surrounding a PHOCS measurement date for stations across the globe,</div><div>and mine this data for observation probability distributions as a function of level altitude, local</div><div>time of day of launch, latitude, etc. These distributions will then be used as Bayesian priors to</div><div>constrain temperature and pressure fits during the oxygen spectral fitting routine. Subsequently,</div><div>these priors will be used to estimate uncertainties in vertically-resolved GHG mixing ratios.</div>