Aerosols, i.e., particulate matter (PM) in the atmosphere, play a key role in radiation transfer in the Earth system. Aerosols scatter or absorb sunlight, thereby cooling or heating atmospheric layers. Individual aerosol particles also act as condensation nuclei or ice nuclei in the troposphere. Therefore, knowledge of the location and optical properties of aerosols is crucial for understanding the thermal balance of the atmosphere.¹

A simple 355-nm high-spectral-resolution lidar (HSRL) is developed for continuous observation of aerosol profiles. A scanning Michelson interferometer is used to separate the Rayleigh and Mie scattering components. The interferometer is periodically scanned in the range of one fringe. Interference contrast, which contains aerosol backscatter information, is estimated at each height through fitting analysis of the scan data. The interference contrast and fringe position are calibrated with the reference signals taken from the transmitted laser. Furthermore, the 1-day continuous measurement of aerosol backscatter and extinction coefficients is demonstrated. Comparison with a nighttime Raman lidar indicates a good performance of the scanning method.

The Japanese Global Observing SATellite for Greenhouse gases and Water cycle (GOSAT-GW) will be an Earth-observing satellite to conduct global observations of atmospheric carbon dioxide (CO₂), methane (CH₄), and nitrogen dioxide (NO₂) simultaneously from a single platform. GOSAT-GW is the third satellite in the series of the currently operating Greenhouse gases Observing SATellite (GOSAT) and GOSAT-2. It will carry two sensors, the Total Anthropogenic and Natural emissions mapping SpectrOmeter-3 (TANSO-3) and the Advanced Microwave Scanning Radiometer 3 (AMSR3), with the latter dedicated to the observation of physical parameters related to the water cycle. TANSO-3 is a high-resolution grating spectrometer designed to measure reflected sunlight in the visible to short-wave infrared spectral ranges. It aims to retrieve the column-averaged dry-air mole fractions of CO₂ and CH₄ (denoted as XCO₂ and XCH₄, respectively), as well as the vertical column density of tropospheric NO₂. The TANSO-3 sensor onboard GOSAT-GW will utilize the wavelength bands of 0.45, 0.76, and 1.61 µm for NO₂, O₂, and CO₂ and CH₄ retrievals, respectively. GOSAT-GW will fly in a sun-synchronous orbit with a local overpass time of approximately 13:30 and a 3-day ground-track repeat cycle. The TANSO-3 sensor has two observation modes in the push-broom operation: Wide Mode, which provides globally covered maps with a 10-km spatial resolution within 3 days, and Focus Mode, which provides snapshot maps over targeted areas with a high spatial resolution of 1–3 km. The objectives of the GOSAT-GW mission include (1) monitoring atmospheric global-mean concentrations of greenhouse gasses (GHGs), (2) verifying national anthropogenic GHG emissions inventories, and (3) detecting GHG emissions from large sources, such as megacities and power plants. A comprehensive validation exercise will be conducted to ensure that the sensor products’ quality meets the required precision to achieve the above objectives. With a projected operational lifetime of seven years, GOSAT-GW will provide vital space-based constraints on both anthropogenic and natural GHG emissions. These measurements will contribute significantly to climate change mitigation efforts, particularly by supporting the Global Stocktake (GST) mechanism, a key element of the Paris Agreement.

Simple dual-wavelength high-spectral-resolution lidar at 355 and 532 nm with a scanning interferometer was developed for continuous observations of aerosol profiles. Scanning the interferometer periodically over a range of one fringe at 532 nm (1.5 fringes at 355 nm) enabled recording of range-resolved interference signals at these two wavelengths. Reference signals taken from the transmitted laser were used to correct the interference phase shift due to laser frequency variation for every scan. Profiles of aerosol backscatter and extinction coefficients were retrieved from range-resolved interference data. One month of continuous measurements demonstrated the robustness of the system.

A simple high spectral resolution lidar technique using a multi-longitudinal mode laser is proposed for measuring aerosol extinction and backscattering coefficients. A scanning interferometer having the same free spectral range as the mode spacing of the laser is used to separate Rayleigh from Mie scattering. Scanning the interferometer in the span of one fringe, the lidar signals at the minimum and maximum Mie-scattering transmission are measured. The Rayleigh scattering signal is analyzed from these signals, and the aerosol extinction coefficient is derived. The interferometer transmittance for Mie scattering is calibrated with the reference signals taken with a portion of the transmitted laser beam.