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he Areal Averaged Albedo VAP yields areal averaged surface spectral albedo estimates from MFRSR measurements collected under fully overcast conditions via a simple one-line equation (Barnard et al., 2008), which links cloud optical depth, normalized cloud transmittance, asymmetry parameter, and areal averaged surface albedo under fully overcast conditions.
The Areal Averaged Albedo VAP yields areal averaged surface spectral albedo estimates from MFRSR measurements collected under fully overcast conditions via a simple one-line equation (Barnard et al., 2008), which links cloud optical depth, normalized cloud transmittance, asymmetry parameter, and areal averaged surface albedo under fully overcast conditions.
We have measured the spectrum of Titan near 5 micrometers and have found it to be dominated by absorption from the carbon monoxide 1-0 vibration-rotation band. The position of the band edge allows us to constrain the abundance of CO in the atmosphere and/or the location of the reflecting layer in the atmosphere. In the most likely case, 5 micrometers radiation is reflected from the surface and the mole fraction of CO in the atmosphere is qCO=10(+10/-5) ppm, significantly lower than previous estimates for tropospheric CO. The albedo of the reflecting layer is approximately 0.07(+0.02/-0.01) in the 5 micrometers continuum outside the CO band. The 5 micrometers albedo is consistent with a surface of mixed ice and silicates similar to the icy Galilean satellites. Organic solids formed in simulated Titan conditions can also produce similar albedos at 5 micrometers.
This study develops an algorithm for representing detailed spectral features of vegetation albedo based on Moderate Resolution Imaging Spectrometer (MODIS) observations at 7 discrete channels, referred to as the MODIS Enhanced Vegetation Albedo (MEVA) algorithm. The MEVA algorithm empirically fills spectral gaps around the vegetation red edge near 0.7 micrometers and vegetation water absorption features at 1.48 and 1.92 micrometers which cannot be adequately captured by the MODIS 7 channels. We then assess the effects of applying MEVA in comparison to four other traditional approaches to calculate solar fluxes and aerosol direct radiative forcing (DRF) at the top of atmosphere (TOA) based on the MODIS discrete reflectance bands. By comparing the DRF results obtained through the MEVA method with the results obtained through the other four traditional approaches, we show that filling the spectral gap of the MODIS measurements around 0.7 micrometers based on the general spectral behavior of healthy green vegetation leads to significant improvement in the instantaneous aerosol DRF at TOA (up to 3.02Wm(exp -2) difference or 48% fraction of the aerosol DRF, .6.28Wm(exp -2), calculated for high spectral resolution surface reflectance from 0.3 to 2.5 micrometers for deciduous vegetation surface). The corrections of the spectral gaps in the vegetation spectrum in the near infrared, again missed by the MODIS reflectances, also contributes to improving TOA DRF calculations but to a much lower extent (less than 0.27Wm(exp -2), or about 4% of the instantaneous DRF). Compared to traditional approaches, MEVA also improves the accuracy of the outgoing solar flux between 0.3 to 2.5 micrometers at TOA by over 60Wm(exp -2) (for aspen 3 surface) and aerosol DRF by over 10Wm(exp -2) (for dry grass). Specifically, for Amazon vegetation types, MEVA can improve the accuracy of daily averaged aerosol radiative forcing in the spectral range of 0.3 to 2.5 micrometers at equator at the equinox by 3.7Wm(exp -2). These improvements indicate that MEVA can contribute to regional climate studies over vegetated areas and can help to improve remote sensing-based studies of climate processes and climate change.
The need for accurate geometric and radiometric information over large areas has become increasingly important. Laser altimetry is one of the key technologies for obtaining this geometric information. However, there are important application areas where the observing platform has its orbit constrained by the other instruments it is carrying, and so the spatial resolution that can be recorded by the laser altimeter is limited. In this paper we show how information recorded by one of the other instruments commonly carried, a high-resolution imaging camera, can be combined with the laser altimeter measurements to give a high resolution estimate both of the surface geometry and its reflectance properties. This estimate has an accuracy unavailable from other interpolation methods. We present the results from combining synthetic laser altimeter measurements on a coarse grid with images generated from a surface model to re-create the surface model.
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Remote techniques for determining albedo are examined in terms of the range of view angles required in the use of string techniques with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the High Resolution Imaging Spectroradiometer (HIRIS). Ground data are used to compute full and half strings out to 15, 30, 45, and 60 degrees for various sun angles and ground cover types. A knowledge-based system is employed to evaluate both the visible and near-IR bands, and the results indicate errors of up to 7 percent for the MODIS data, HIRIS data, and the full-string +/- 60 degrees. In the cases of large extrapolations greater ranges of error are noted indicating that 60-deg systems are most effective. The error is increased in the case of sensor systems that only view in the fore or aft direction, and the MODIS full string for +/- 45 deg is also considered a good system.
We have analyzed three EPIC images during the annular solar eclipse on June 21, 2020 when centers of the eclipse were in the Arabian Peninsula (mostly desert), the Himalayas (mostly barren land), and China (mostly cloudy over vegetation) and compared with two images for 2017 American solar eclipse over Casper, WY and Columbia, MO (vegetated surface for both). We found that the global average reductions of spectral reflectance for the three images during 2020 solar eclipse are quite different while the reductions of spectral reflectance for the two images for 2017 solar eclipse are similar. Radiative transfer model simulations suggest that different surface spectral albedo and cloud fraction attribute to the different reduction of spectral reflectance for three images during 2020 eclipse while similar spectral albedo of vegetated surface around Casper and Columbia are the main cause for the similar spectral reflectance reduction for the two images during 2017 solar eclipse.
Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centered over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700+/-50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948-2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade. Subject terms: Earth sciences Atmospheric science Climate science
Actinometric observations of albedo radiation absorption
Planetary albedo as affected by solar radiation reflected from surface of red clay soil or white quartz sand
Over the extreme temperature variations experienced in a single lunar day (∆T≈300 K), particular minerals common to the lunar surface show spectral changes at near-infrared wavelengths in laboratory settings (Singer and Roush, 1985; Roush and Singer, 1986, 1987). Variations in temperature can cause variations in the size and shape of crystallographic sites, which control the position, shape, and depth of crystal field absorptions. At an observation wavelength of 1064 nm, the Lunar Orbiter Laser Altimeter (LOLA) should be highly sensitive to temperature-dependent changes of orthopyroxene. Here we analyze temperature-dependent spectral changes of the lunar surface as measured from orbit by LOLA. We couple LOLA measurements of normal albedo with measurements of surface temperature from the Diviner Lunar Radiometer Experiment, analyzing the maria and highlands terranes between ±50° in 1°x1° spatial bins. We provide the first evidence of temperature-dependent spectral changes on the lunar surface from orbital observations, finding that the majority of the lunar surface between 50°N and 50°S demonstrates a small, yet measurable, negative change in normal albedo at 1064 nm with temperature (-∆R/∆T). The measurable effect is on the order of a few percent change in reflectance per ~80 K, indicating temperature changes do not have a large effect on measurements of albedo at the sensitivity of the LOLA instrument. Stronger -∆R/∆T values tend to be associated with the maria, and regions with elevated orthopyroxene levels. Our results suggest that single-wavelength lasers may be powerful tools for understanding the distribution of particular minerals on the lunar surface.
The solar radiation must be considered as the primary factor when we study the climatic system because it provides almost all energy that drives the climatic system and most atmospheric phenomena. The solar radiation at the TOA is partially transferred, transformed into other forms of energy that are eventually dissipated by the general circulation of the atmosphere and oceans, and partially used in chemical and biological processes. The absorption of solar energy in the atmosphere (Acol) plays a key role in the climate system, not only because it affects the amount of solar energy absorbed by the Earth system, but also because it changes the vertical distribution of absorbed energy, which in turn impacts surface evaporation, atmospheric convection and precipitation. To investigate Acol, we have collected the collocated satellite-surface observations over the 35 selected BSRN surface sites during the period 2000-2004. The surface radiation budgets are averaged from the BSRN Shortwave (SW) observations over a 1-hour interval centered at the time of the NASA Terra and Aqua satellites overpass, and the TOA radiation budgets are averaged from the closest FOV satellite data to the BSRN stations. Then the atmospheric column SW absorption will be inferred from the satellite TOA albedo and BSRN surface absorption (through the estimated surface albedo). Monthly means of Acol, TOA albedo, and surface absorption have been calculated under both clear- and all-sky conditions over the 35 selected BSRN sites which represent different climate regimes. To evaluate the GCM simulations, we have collected the ECHAM5-HAM simulated surface, TOA and atmospheric radiation budgets by researchers at ETH Zurich and compared those simulations with observations. The preliminary comparisons have shown that the ECHAM5 simulated clear-sky surface absorption, TOA albedo, and ACOL agree very well (1-3%) with observations. Under all-sky conditions, they have strong correlations with CERES-derived cloud fraction. The simulated surface absorption is lower and TOA albedo is higher than those under clear skies, but ACOL does not increase too much. However, there are relatively large differences over some regions and months. A further study is needed.
An atmospheric solar radiation model has been coupled with surface reflectance measurements for two vegetation types, pasture land and savannah, in order to address several issues associated with understanding the directional planetary albedo; i.e., the dependence of planetary albedo upon solar zenith angle. These include an elucidation of processes that influence the variation of planetary albedo with solar zenith angle, as well as emphasizing potential problems associated with converting narrowband planetary albedo measurements to broadband quantities. It is suggested that, for vegetated surfaces, this latter task could be somewhat formidable, since the model simulations indicate that narrowband to broadband conversions strongly depend upon vegetation type. A further aspect of this paper is to illustrate a procedure by which reciprocity inconsistencies within a bidirectional reflectance dataset, if they are not too severe, can be circumvented.
We investigate the depth, variability, and history of regolith on asteroid Vesta using data from the Dawn spacecraft. High-resolution (15-20 m pixel(sup -1)) Framing Cameraimages are used to assess the presence of morphologic indicators of a shallow regolith,including the presence of blocks in crater ejecta, spur-and-gully-type features in crater walls,and the retention of small (less than 300 m) impact craters. Such features reveal that the broad,regional heterogeneities observed on Vesta in terms of albedo and surface composition extend to the physical properties of the upper approx. 1 km of the surface. Regions of thin regolithare found within the Rheasilvia basin and at equatorial latitudes from approx. 0-90 deg. E and approx.260-360 deg. E. Craters in these areas that appear to excavate material from beneath the regolithhave more diogenitic (Rheasilvia, 090 deg. E) and cumulate eucrite (260-360 deg. E) compositions.A region of especially thick regolith, where depths generally exceed 1 km, is found from approx.100-240 deg. E and corresponds to heavily cratered, low-albedo surface with a basaltic eucritecomposition enriched in carbonaceous chondrite material. The presence of a thick regolithin this area supports the idea that this is an ancient terrain that has accumulated a larger component of exogenic debris. We find evidence for the gardening of crater ejecta towardmore howarditic compositions, consistent with regolith mixing being the dominant form of "weathering" on Vesta.
Photometric and spectra analysis of data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) has yielded intriguing findings regarding the surface properties of several of the icy Saturnian satellites. Spectral cubes were obtained of these satellites with a wavelength distribution in the IR far more extensive than from any previous observations. Disk-integrated solar phase curves were constructed in several key IR wavelengths that are indicative of key properties of the surface of the body, such as macroscopic roughness, fluffiness (or the porosity of the surface), global albedo and scattering properties of surface particles. Polynomial fits to these phase curves indicate a linear albedo trend of the curvature of the phase functions. Rotational phase functions from Enceladus were found to exhibit a double-peaked sinusoidal curve, which shows larger amplitudes for bands corresponding to water ice and a linear amplitude-albedo trend. These functions indicate regions on the surface of the satellite of more recent geologic activity. In addition, recent images of Enceladus show tectonic features and an absence of impact craters on Southern latitudes which could be indicative of a younger surface. Investigations into the properties of these features using VIMS are underway.
The MicaSense Altum imager is an off-the-shelf, synchronized multispectral and thermal camera, combined with a Global Positioning System (GPS) unit and downwelling light sensor (DLS). The Altum takes images of the land surface within its field of view (FOV) across five visible bands and one longwave infrared thermal band. The sensor records the radiance and converts it to digital numbers. Imagery is radiometrically corrected, taking into account the sensor calibration, lens distortions, vignette effects, sun angle, and atmospheric effects (scattering and absorption). The photogrammetry software Agisoft PhotoScan v 1.4 is used to align and stitch the images into a larger composite image using the technique of structure from motion image capture to construct a dense cloud and 3D model of the surface, which is used to produce a digital elevation model of the terrain surveyed and orthomosaic imagery. Land surface leaf area index, albedo, and surface skin temperature are provided for the user. The user can perform raster calculations on the imagery to produce various other vegetative indices, which are used to indicate plant health and land surface characteristics, including Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Water Index (NDWI), surface temperature, and Enhanced_vegetation_index (EVI). This code is provided with the readme file for each data set. The images have a resolution of 20-60 cm/pixel, which are subsampled to 100 cm/pixel.