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  • 1
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    The Challenges of Measuring Methane from Space with a Lidar (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The global and regional quantification of methane fluxes and identification of its sources and sinks has been highlighted as one of the goals of the NASA 2017 Earth Science Decadal Survey. Detecting methane from space and airborne platforms with an active (laser) remote sensing instrument presents several unique technology and measurement challenges. The instrument must have a single frequency, narrow-linewidth light source, and photon-sensitive detector at the right spectral region to make continuous measurements from orbit, day and night, all seasons and at all latitudes. It must have a high signal to noise ratio and must be relatively immune to biases from aerosol/cloud scattering, spectroscopic and meteorological data uncertainties, and instrument systematic errors. At Goddard Space Flight Center (GSFC), in collaboration with industry, we have developed an airborne instrument to measure methane. Our instrument is a nadir-viewing lidar that uses Integrated Path Differential Absorption (IPDA), to measure methane near 1.65 m. We sample the absorption line using multiple wavelengths from a narrow linewidth laser source and a sensitive photodetector. This measurement approach provides maximum information content about the CH4 column, and minimizes biases in the XCH4 retrieval. In this paper, we will review our progress to date and discuss the technology challenges, options and tradeoffs to measure methane from space and airborne platforms.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN61056 , International Conference on Space Optics (ICSO) 2018; Oct 09, 2018 - Oct 12, 2018; Chania; Greece
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    A New Definition of the South‐East Madagascar Bloom and Analysis of Its Variability (2019)
    Wiley | AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 124 (3). pp. 1717-1735.
    Details
    Publication Date: 2022-01-31
    Description: The South-East Madagascar Bloom occurs in an oligotrophic region of the southwest Indian Ocean. Phase locked to austral summer, this sporadic feature exhibits substantial temporal and spatial variability. Several studies, with different hypotheses, have focused on the initiation mechanism triggering the bloom, but none has been as yet clearly substantiated. With 19 years of ocean color data set available as well as in situ measurements (Argo profiles), the time is ripe to review this feature. The bloom is characterized in a novel manner, and a new bloom index is suggested, yielding 11 bloom years, including 3 major bloom years (1999, 2006, and 2008). Spatially, the bloom varies from a mean structure (22–32°S; 50–70°E) both zonally and meridionally. A colocation analysis of Argo profiles and chlorophyll-a data revealed a bloom occurrence in a shallow-stratified layer, with low-salinity water in the surface layers. Additionally, a quantitative assessment of the previous hypotheses is performed and bloom occurrence is found to coincide with La Niña events and reduced upwelling intensity south of Madagascar. A stronger South-East Madagascar Current during La Niña may support a detachment of the current from the coasts, dampening the upwelling south of Madagascar, and feeding low-salinity waters into the Madagascar Basin, hence increasing stratification. Along with abundance of light, these provide the right conditions for a nitrogen-fixing cyanobacterial phytoplankton bloom onset
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 3
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    A Model Investigation of the Influences of the South‐East Madagascar Current on the South‐East Madagascar Bloom (2020)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-02-08
    Description: The South-East Madagascar Bloom, one of the most compelling biogeochemical features of the Indian Ocean, occurs sporadically during austral summer in the oligotrophic waters south-east of Madagascar, where it can cover up to 1% of the global ocean surface area. Its spatial extension and its timing are highly variable. A high-resolution biophysical model is used to investigate a previous hypothesis that the onset of a particular circulation of the South-East Madagascar Current advects fresher and nutrient-rich waters eastward, feeding the bloom. The model is able to reproduce an intermittent phytoplankton bloom with large spatial variability but in the subsurface layers, as well as the presence of an irregular retroflection of the South-East Madagascar Current. The simulated bloom occurs within a shallow stratified mixed layer, with fresher waters at the surface, parallel to the water mass in an observed bloom. The model results suggest, from a nutrient flux analysis, that horizontal advection of low-salinity nutrient-rich Madagascan coastal waters can indeed trigger a phytoplankton bloom. The coupled model is also able to resolve a bloom that is atmospherically forced by cyclonic activity.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
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