Retrieval and Uncertainty Analysis of Land Surface Reflectance Using a Geostationary Ocean Color Imager

Land surface reflectance (LSR) is well known as an essential variable to understand land surface properties. The Geostationary Ocean Color Imager (GOCI) be able to observe not only the ocean but also the land with the high temporal and spatial resolution thanks to its channel specification. In this study, we describe the land atmospheric correction algorithm and present the quality of results through comparison with Moderate Resolution Imaging Spectroradiometer (MODIS) and in-situ data for GOCI-II. The GOCI LSR shows similar spatial distribution and quantity with MODIS LSR for both healthy and unhealthy vegetation cover. Our results agreed well with in-situ-based reference LSR with a high correlation coefficient (>0.9) and low root mean square error (<0.02) in all 8 GOCI channels. In addition, seasonal variation according to the solar zenith angle and phenological dynamics in time-series was well presented in both reference and GOCI LSR. As the results of uncertainty analysis, the estimated uncertainty in GOCI LSR shows a reasonable range (<0.04) even under a high solar zenith angle over 70°. The proposed method in this study can be applied to GOCI-II and can provide continuous satellite-based LSR products having a high temporal and spatial resolution for analyzing land surface properties.

Monte Carlo Radiative Transfer Simulation to Analyze the Spectral Index for Remote Detection of Oil Dispersed in the Southern Baltic Sea Seawater Column: The Role of Water Surface State

The article presents the results of simulations that take into account the optical parameters of the selected sea region (from literature data on the southern Baltic Sea) and two optically extreme types of crude oil (from historical data) which exist in the form of a highly watered-down oil-in-water emulsion (10 ppm). The spectral index was analyzed based on the results of modeling the radiance reflectance distribution for almost an entire hemisphere of the sky (zenith angle from 0 to 80°). The spectral index was selected and is universal for all optically different types of oil (wavelengths of 650 and 412 nm). The possibility of detecting pollution in the conditions of the wavy sea surface (as a result of wind of up to 10 m/s) was studied. It was also shown that if the viewing direction is close to a direction perpendicular to the sea surface, observations aimed at determining the spectral index are less effective than observations under the zenith angle of incidence of sunlight for all azimuths excluding the direction of sunlight’s specular reflection.

Bestimmung optischer Dichten stratosphärischer Aerosole aus den Farbverhältnissen historischer Gemälde – kann das funktionieren?

&lt;p&gt;Die M&amp;#246;glichkeit, quantitative Information &amp;#252;ber die stratosph&amp;#228;rische Aerosolbefrachtung &amp;#8211; insbesondere in Zeitr&amp;#228;umen vulkanisch verst&amp;#228;rkter Aerosole &amp;#8211; aus den Farbverh&amp;#228;ltnissen historischer Gem&amp;#228;lde abzuleiten, erscheint auf den ersten Blick sehr vielversprechend. Tats&amp;#228;chlich wurde dieser Ansatz in einigen Studien verwendet, um die optische Dichte stratosph&amp;#228;rischer Aerosole nach st&amp;#228;rkeren Vulkanausbr&amp;#252;chen &amp;#252;ber einen Zeitraum von ca. 500 Jahren zu bestimmen. In diesem Vortrag evaluieren wir die Verl&amp;#228;sslichkeit dieses Ansatzes mit Hilfe von Simulationen mit dem Strahlungstransfermodell SCIATRAN und sch&amp;#228;tzen die Fehler der abgeleiteten optischen Dichten basierend auf plausiblen Unsicherheiten relevanter Parameter ab. Wir zeigen, dass die Unsicherheiten in einigen wichtigen Parametern &amp;#8211; die f&amp;#252;r historische Eruptionen typischerweise nur unzureichend bekannt sind &amp;#8211; zu &amp;#228;hnlichen Ver&amp;#228;nderungen in den Rot-Gr&amp;#252;n-Farbverh&amp;#228;ltnissen f&amp;#252;hren k&amp;#246;nnen wie massive Vulkanausbr&amp;#252;che (z.B. des Tambora 1815 oder des Krakatao 1883). Von den untersuchten Effekten hat die angenommene Gr&amp;#246;&amp;#223;enverteilung der stratosph&amp;#228;rischen Aerosole den gr&amp;#246;&amp;#223;ten Einfluss auf die Farbverh&amp;#228;ltnisse und damit die abgeleiteten optischen Dichten. F&amp;#252;r Sonnenzenitwinkel (SZA von engl. Solar Zenith Angle) von mehr als 80 Grad kann auch die angenommene stratosph&amp;#228;rische Ozonmenge die abgeleiteten optischen Dichten signifikant beeinflussen. F&amp;#252;r SZA gr&amp;#246;&amp;#223;er als 90 Grad weisen die horizontnahen Farbverh&amp;#228;ltnisse eine dramatische Abh&amp;#228;ngigkeit vom SZA auf, so dass f&amp;#252;r diese F&amp;#228;lle eine Bestimmung optischer Dichten praktisch unm&amp;#246;glich ist. Abschlie&amp;#223;end gehen wir auf die Frage ein, wie stark die langfristige Ver&amp;#228;nderung der Farben eines Gem&amp;#228;ldes die optischen Dichten beeinflussen kann.&lt;/p&gt;

Scan strategies for wind profiling with Doppler lidar – An LES-based evaluation

Lidar scan techniques for wind profiling rely on the assumption of a horizontally homogeneous wind field and stationarity for the duration of the scan. As this condition is mostly violated in reality, detailed knowledge of the resulting measurement error is required. The objective of this study is to quantify and compare the expected error associated with Doppler-lidar wind profiling for different scan strategies and meteorological conditions by performing virtual measurements implemented in a large-eddy simulation (LES) model. Various factors influencing the lidar retrieval error are analyzed through comparison of the wind measured by the virtual lidar with the ‘true’ value generated by the LES. These factors include averaging interval length, zenith angle configuration, scan technique and instrument orientation. For the first time, ensemble simulations are used to determine the statistically expected uncertainty of the lidar error. The analysis reveals a root-mean-square deviation (RMSD) of less than 1 m s−1 for 10 min averages of wind speed measurements in a moderately convective boundary layer, while RMSD exceeds 2 m s−1 in strongly convective conditions. Unlike instrument orientation and scanning scheme, the zenith angle configuration proved to have significant effect on the retrieval error. Horizontal wind speed error is reduced when a larger zenith angle configuration is used, but is increased for measurements of vertical wind. Results suggest that the scan strategy has a relevant effect on the lidar retrieval error and that instrument configuration should be chosen depending on the quantity of interest and the flow conditions in which the measurement is performed.

Monte Carlo Radiative Transfer Simulation to Analyze the Spectral Index for Remote Detection of Oil Dispersed in the Southern Baltic Sea Seawater Column: The Role of Water Surface State

The presented results of simulations take into account the optical parameters of the selected sea region (from literature data on the southern Baltic Sea) and two optically extreme types of crude oil (from historical data) which exist in the form of a highly diluted oil-in-water emulsion (10 ppm). The spectral index was analyzed based on the results of modelling the radiance reflectance distribution for almost an entire hemisphere of the sky (zenith angle from 0 to 80o). The spectral index was selected and is universal for all optically different types of oil (wavelengths 650 and 412 nm). The possibility of detecting pollution in the conditions of the wavy sea surface (as a result of wind of up to 10 m/s) was studied. It has been also shown that if the viewing direction is close to a direction perpendicular to the sea surface, observations aimed at determining the spectral index are less effective than observation under the zenith angle of incidence of sunlight for all azimuths excluding the direction of sunlight specular reflection.

On the relationship between energy input to the ionosphere and the ion outflow flux under different solar zenith angles

The ionosphere is one of the important sources for magnetospheric plasma, particularly for heavy ions with low charge states. We investigate the effect of solar illumination on the number flux of ion outflow using data obtained by the Fast Auroral SnapshoT (FAST) satellite at 3000–4150 km altitude from 7 January 1998 to 5 February 1999. We derive empirical formulas between energy inputs and outflowing ion number fluxes for various solar zenith angle ranges. We found that the outflowing ion number flux under sunlit conditions increases more steeply with increasing electron density in the loss cone or with increasing precipitating electron density (> 50 eV), compared to the ion flux under dark conditions. Under ionospheric dark conditions, weak electron precipitation can drive ion outflow with small averaged fluxes (~ 107 cm−2 s−1). The slopes of relations between the Poynting fluxes and outflowing ion number fluxes show no clear dependence on the solar zenith angle. Intense ion outflow events (> 108 cm−2 s−1) occur mostly under sunlit conditions (solar zenith angle < 90°). Thus, it is presumably difficult to drive intense ion outflows under dark conditions, because of a lack of the solar illumination (low ionospheric density and/or small scale height owing to low plasma temperature). Graphical abstract

FREE STATION TASK WITH DRONE

Using drones with different purposes than only taking photos is nowadays the main direction of drone development. Drones are made for package delivery, people transport, etc. Drone equipped by GNSS RTK and prism can be used as orientation point for the free station. The idea is using drone to get coordinates of total stations inappropriate for GNSS. such as high buildings and forest. The drone can fly above the obstacle causing inappropriate, so the GNSS will compute the position coordinates correctly. Total station will measure distance and angles on prism to get free station coordinates. This article deals with the accuracy of using two points in the free station task. Accuracy of measurement and data is based on real values. Drone can be used as the target if it is not windy, the position accuracy of the target on drone is 5 cm. Wind has no effect on the vertical position accuracy of the the drone. The results show that the same principles and limitations must be observed when measuring the free station task. Horizontal angle between orientation points must be bigger than 100 gon and the zenith angle must be at least 50 gon. The distance between orientation and free station must longer than consequent measured points.

Top-of-atmosphere albedo bias from neglecting three-dimensional cloud radiative effects

Clouds cover on average nearly 70% of Earth’s surface and regulate the global albedo. The magnitude of the shortwave reflection by clouds depends on their location, optical properties, and three-dimensional (3D) structure. Due to computational limitations, Earth system models are unable to perform 3D radiative transfer calculations. Instead they make assumptions, including the independent column approximation (ICA), that neglect effects of 3D cloud morphology on albedo. We show how the resulting radiative flux bias (ICA-3D) depends on cloud morphology and solar zenith angle. We use high-resolution (20–100 m horizontal resolution) large-eddy simulations to produce realistic 3D cloud fields covering three dominant regimes of low-latitude clouds: shallow cumulus, marine stratocumulus, and deep convective cumulonimbus. A Monte Carlo code is used to run 3D and ICA broadband radiative transfer calculations; we calculate the top-of-atmosphere (TOA) reflected flux and surface irradiance biases as functions of solar zenith angle for these three cloud regimes. Finally, we use satellite observations of cloud water path (CWP) climatology, and the robust correlation between CWP and TOA flux bias in our LES sample, to roughly estimate the impact of neglecting 3D cloud radiative effects on a global scale. We find that the flux bias is largest at small zenith angles and for deeper clouds, while the albedo bias is most prominent for large zenith angles. In the tropics, the annual-mean shortwave radiative flux bias is estimated to be 3.1±1.6 W m−2, reaching as much as 6.5 W m−2 locally.