Change In Solar Absorptance Research Articles

Observed Energetic Adjustment of the Arctic and Antarctic in a Warming World

Abstract Satellite observations reveal that decreasing surface albedo in both polar regions is increasing the absorption of solar radiation, but the disposition of this absorbed energy is fundamentally different. Fluxes of absorbed solar radiation, emitted thermal radiation, and net energy imbalances are assessed for both polar regions for the last 21 years in the Clouds and Earth’s Radiant Energy System record. Arctic absorbed solar radiation is increasing at 0.98 ± 0.69 W m−2 decade−1, consistent with the anticipated response to sea ice loss. However, Arctic thermal emission is responding at a similar rate of 0.94 ± 0.55 W m−2 decade−1. This is surprising since the radiative impact of ice loss would be expected to favor increasing solar absorption. We find however, that clouds substantially mask trends in Arctic solar absorption relative to clear sky while having only a modest impact on thermal emission trends. As a result, the Arctic net radiation imbalance has not changed over the period. Furthermore, variability of absorbed solar radiation explains two-thirds of the variability in annual thermal emission suggesting that Arctic thermal fluxes rapidly adjust to offset changes in solar absorption and re-establish equilibrium. Conversely, Antarctic thermal emission is not responding to the increasing (although not yet statistically significant) solar absorption of 0.59 ± 0.64 W m−2 decade−1 with less than a third of the annual thermal variability explained by accumulated solar absorption. The Arctic is undergoing rapid adjustment to increasing solar absorption resulting in no change to the net energy deficit, while increasing Antarctic solar absorption represents additional energy input into the Earth system. Significance Statement The polar regions of Earth are undergoing ice loss through ongoing global warming, reducing the ice cover and decreasing solar reflectivity, which would be expected to warm these regions. We use satellite observations to measure the trends in solar absorption and emitted thermal radiation over the Arctic and Antarctic for the last two decades. Arctic thermal emission is increasing at a compensating rate to solar absorption with a close relationship between these processes. Conversely, Antarctic thermal emission is not responding to solar absorption demonstrating that Antarctic surface temperatures are not significantly influenced by the region’s reflectivity. The Arctic is undergoing rapid adjustment to increasing solar absorption through warming, while increasing Antarctic solar absorption represents additional energy input into the Earth system.

Thermo-Optical Property Degradation of ITO-Coated Aluminized Polyimide Thin Films Under VUV and Low-Energy Proton Radiation

We studied thermo-optical property degradation of indium tin oxide (ITO)-coated aluminized polyimide thin films under exposure to vacuum ultraviolet radiation and low-energy (3 and 5 keV) protons during ground tests using the Complex Irradiation Facility at the DLR site in Bremen. Changes in solar absorption and thermal emission coefficients caused by the irradiation were analyzed. We report a significant increase in solar absorptance of the samples irradiated by protons. We also attempted to identify any defects on the surface of the samples. The study was motivated by a unique opportunity that is provided by the Complex Irradiation Facility to study the degradation effects induced by exposure to protons with an energy below 10 keV and short-wavelength light below 115 nm.

The degradation kinetics of the optical properties under proton irradiation for ZnO pigments modified by Al2O3 and Al2O3·CeO 2 nanopowders

The effects of proton exposure (100 keV, 5×1014–1×1016 cm−2) on the reflective spectra within the wavelength ranged from 250 to 2500 nm of the zinc oxide pigments modified by Al2O3 and Al2O3·CeO 2 nanopowders were investigated. It has been established that the introduction of nanopowders can enhance the optical stability of the pigments under proton irradiation due to the decrease in vacancies concentration of zinc and oxygen (V, V, V) and interstitial oxygen (O). Expected values of change in solar absorptance and solar reflectance caused by single radiation-induced defects were calculated to simulate 20 years of proton exposure on the circular orbit (R=20, 000 km).

A study on damage effects of

The changes in optical properties and damage mechanism of ZnO/silicone white paint caused by <200 keV protons in space were investigated in terms of ground-based simulation testing. The energies of protons were chosen as 50, 90, and 110 keV. The results show that the change in solar absorptance s increases with increasing irradiation fluence as well as the proton energy. On the basis of photoluminescence spectroscopy, it is revealed that with increasing proton fluence, the 660-nm emission band related to the interstitial Zn-ions changes little, the 405-nm emission band related to the Zn vacancies decreases and tends to disappear, the 460-nm emission band related to the double ionized oxygen vacancies VO  decreases, and the emission band

An analysis on optical degradation of ZnO/silicone white paint under proton exposure

The optical degradation mechanism of ZnO/silicone white paint caused by 50 keV protons was investigated in terms of X-ray photoelectron spectroscopy (XPS). The results show that the change in solar absorptance Δ α s increases with increasing proton fluence, and the variation of Δ α s has a good relationship with the formation of the oxygen vacancies in ZnO and the Si–C O functional groups in silicone binder. With increasing the proton fluence, both the area ratio of lattice oxygen peak to XPS O 1s spectrum and the peak area in Zn 3d spectra decrease, indicating that the percentage of lattice oxygen decreases and the amount of oxygen vacancies increases. Meanwhile, the area ratio of the Si–C O peak to XPS Si 2p spectrum increases, demonstrating the formation of Si–C O chromophores in silicone binder. Both the oxygen vacancies and the Si–C O chromophores can lead to an optical degradation of ZnO/silicone white paint under proton exposure.

Analysis of Metallized TeflonTM Thin-Film Materials Performance on Satellites

Laboratory and on-orbit performance data for two common thermal control materials, silver- and aluminum-backed (metallized) fluorinated ethyl-propylene, were collected from a variety of sources and analyzed. It is demonstrated that the change in solar absorptance α is a strong function of particulate radiation for these materials. Examination of additional data shows that the atomic-oxygen recession rate is a strong function of solar exposure with an induction period of between 25 to 50 equivalent solar hours. The relationships determined in this analysis were incorporated into an electronic knowledge base, the Spacecraft Materials Selector, under NASA Contract NAS8-98213. This tool is available from the NASA Space Environments and Effects program office.

Electron, Proton, and Ultraviolet Radiation Effects on Thermophysical Properties of Polymeric Films

The response of coated thin polymer films to simultaneous ultraviolet, electron, and proton radiation has been evaluated by selected measurements in situ and in the laboratory. Exposures simulated the radiation environment near the Earth-sun Lagrangian points 1 and 2 for five years and ∼1000 ultraviolet equivalent solar hours. Materials evaluated were both commercially available and newly developed aromatic polyimide films aluminized on one side and exposed as second surface mirrors. Effects on solar absorptance, thermal emittance, and tensile properties were measured. The in situ changes in solar absorptance of Kapton® and Upilex® were less than 0.1, whereas the solar absorptance of TOR and CP films increased by more than 0.3 without saturating. Thermal emittance measurements also showed that the Kapton and Upilex materials increased only 1-2%, but the remaining materials increased 5-8%. Tensile property measurements made in air following the test showed the failure stress of every type of polymer film decreased as a result of irradiation.

Effect of electron exposure on optical properties of aluminized polyimide film

The effect of the irradiation of electrons with 10–70 keV on optical properties, including spectral reflectance ρ and solar absorptance as, of aluminized polyimide films was investigated. The spectral reflectance was measured in situ before and after electron exposure. Experimental results showed that the reflective properties of aluminized polyimide film were apparently degraded in the 500–1200 nm wavelength range of the solar spectrum. Under the exposure of electrons, no charging effects were found on the aluminized polyimide film serving as an ion-conductive polymer. After the exposure, an “annealing” or “bleaching” effect occurred. At a given irradiation fluence, the change in solar absorptance (Δas) of the aluminized polyimide film was increased with electron energy. There is a threshold value of electron flux φcr which affects the change in Δas of the aluminized polyimide film, approximately φcr = 6 × 1012 electrons/cm2s. When φ &lt; φcr, the change in Δas is independent from the flux; when φ &gt; φcr, Δas increases with the flux monotonically. The change in Δas with electron fluence Φ can be expressed in the form of a power function: Δas = αΦβ. The factors α and β are related to electron energy and show a maximum and a minimum value at 50 keV, respectively.

The impact of optical and thermal properties on the performance of flat plate solar collectors

The impact of the optical properties on the annual performance of flat plate collectors in a Swedish climate has been estimated with the MINSUN program. The collector parameters were determined with a theoretically based calculation program verified from laboratory measurements. The importance of changes in solar absorptance and thermal emittance of the absorber, the addition of a teflon film or a teflon honeycomb, antireflection treatment of the cover glazing and combinations of these improvements were investigated. The results show that several improvements can be achieved for solar thermal absorbers. A combined increase in absorptance from 0.95 to 0.97 and a decrease in emittance from 0.10 to 0.05 increase the annual performance with 6.7% at 50 °C operating temperature. The increase in performance by installing a teflon film as second glazing was estimated to 5.6% at 50 °C. If instead a teflon honeycomb is installed, a twice as high performance increase is obtained, 12.1%. Antireflection treatment of the cover glazing increases the annual output with 6.5% at 50 °C. A combination of absorber improvements together with a teflon honeycomb and an antireflection treated glazing results in a total increase of 24.6% at 50 °C. Including external booster reflectors increases the expected annual output at 50 °C to 19.9–29.4% depending on reflector material.

Effects of Vacuum Ultraviolet Radiation on Thin Polyimide Films

This paper describes the vacuum ultraviolet (VUV) radiation durability screening testing of thin (12.7–25.4 μm) polyimide films proposed for use on the Next Generation Space Telescope (NGST) sunshield. Materials included in this screening test were Kapton®E, Kapton®HN, Upilex®S, CP1, CP1 with vapour deposited aluminium (VDA) on its back surface, and CP2 with a VDA coating on its back surface. Samples were exposed to approximately 1000 equivalent sun hours (ESH) of VUV radiation and examined for changes in solar absorptance, thermal emittance, ultimate tensile strength, and elongation at failure. Changes in the solar absorptance were observed for some materials, and, additionally, significant changes in spectral reflectance were observed in the ultraviolet to visible wavelength region for all of the polyimide materials tested. Changes in the ultimate tensile strength and elongation at failure were within the experimental uncertainty for all samples. Longer exposures are needed to verify the observed trends and to develop performance predictions for these materials on the NGST sunshield.

Characterization of black nickel solar absorber coatings electroplated in a nickel chlorine aqueous solution

Black nickel coatings electroplated in a nickel- and sodium chlorine aqueous solution have been prepared and parameters in the process have been optimized to achieve optimal solar selectivity. The best result is a solar absorptance of 0.96 and a thermal emittance of 0.10, as also has been obtained previously for the same type of coating [1]. Characterization by means of X-ray photo-electron spectroscopy (XPS), scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), Rutherford backscattering (RBS) and 1H( 15N, αγ) 12C nuclear resonance reaction (NRR) have contributed with new information about surface chemical composition, morphology and atomic composition in depth profile. These investigations reveal that the coating is porous and contains mainly metallic nickel at the substrate–coating interface and mainly nickel hydroxide at the front surface. The stability of the coating has been tested regarding high-temperature and condensation at high humidity. It has been found that the solar absorptance changes initially, during the first hour of exposure at high temperature, but will then stabilize. Condensation causes a more severe attack on the coating by cracking it. This is contradictory to the results from previous tests at high temperature and humidity in which the black nickel coating was found to be resistant [1].

Contamination effect of MMH/N2O4 rocket plume product deposit

The predominant species in the plume residue resulting from the incomplete combustion of MMH and N2O4 during the pulse mode operation of the bipropellant motors has been found to be monomethylhydrazine nitrate (MMH-HNO3). At orbital altitude, it is also the most detrimental condensible matter as other species in the plume product or unburned propellant droplets have vapor pressures too high to be of concern. Quantitative data on contamination effects from the MMH/N2O4 thrusters in pulse mode operations are limited. This paper reports experiments in which several types of thermal control surfaces were systematically contaminated with a range of amounts of synthesized MMH-HNO3, after which the resulting change in solar absorptance was measured. Limited experiments were also made to measure the change of solar transmittance of fused silica disks.

Cost-effective method for measuring contamination effects

A simple experimental method is demonstrated for determining the change in solar absorptance (av) of contaminated spacecraft surfaces as a function of deposit surface density. The method applies to contamination originating as material outgassing or vaporization. A quartz crystal microbalance is used to monitor the amount of contaminant condensing on a test thermal control surface in vacuum. Test surface spectral reflectance is measured in the laboratory environment before and after contamination using a standard laboratory spectrophotometer. Reflectance is integrated over the solar spectrum to obtain «5. The data clearly show the relationship between <xs and contaminant mass per unit area. The observed data scatter appears to be assignable totally to the spectrophotometer measurements.