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采用对照反演比法对比分析了青藏高原地区相同时空条件下的MODIS反照率当量反演结果和全反演结果的差异。利用2002—2004年青藏高原地区Terra MODIS数据开展的对照反演试验表明:(1)黑空反射率BSA两种反演结果的绝对偏差小于0.03,白空反射率WSA两种反演结果的绝对偏差约为0.04;BSA两种反演结果绝对偏差的标准差约为0.05,而WSA的则更大。(2)BSA两种反演结果和WSA两种反演结果的绝对偏差及其标准差均存在一定的年际差异。(3)可见光区反照率两种反演结果的绝对偏差及其标准差一般大于红外光区两种反演结果的绝对偏差及其标准差。(4)两种地表反照率反演结果的绝对偏差及其标准差在青藏高原地区三种主要地表类型的差异不大。 相似文献
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Using reflectance values from the seven MODIS “land” bands with 250 or 500 m resolution, along with a corresponding cloud product, we estimate the fraction of each 500 m pixel that snow covers, along with the albedo of that snow. The daily products have data gaps and errors because of cloud cover and sensor viewing geometry. Rather than make users interpolate and filter these patchy daily maps without completely understanding the retrieval algorithm and instrument properties, we use the daily time series to improve the estimate of the measured snow properties for a particular day. We use a combination of noise filtering, snow/cloud discrimination, and interpolation and smoothing to produce our best estimate of the daily snow cover and albedo. We consider two modes: one is the “predictive” mode, whereby we estimate the snow-covered area and albedo on that day using only the data up to that day; the other is the “retrospective” mode, whereby we reconstruct the history of the snow properties for a previous period. 相似文献
4.
The highest resolution images of Comet 19P/Borrelly show many dark features which, upon casual inspection, appear to be low albedo markings, but which may also be shadows or other photometric variations caused by a depression in the local topography. In order to distinguish between these two possible interpretations we conducted a photometric analysis of three of the most prominent of these features using six of the highest quality images from the September 22, 2001 Deep Space 1 (DS1) flyby. We find that: 1. The radiance in the darkest parts of each feature increases as phase angle decreases, similarly to the radiance behavior of the higher albedo surrounding terrain. The dark features could be either fully illuminated low albedo spots or, alternatively, they could be depressions. No part of any of the three regions was in full shadow. 2. One of the regions has a radiance profile consistent with a rimmed depression, the second, with a simple depression with no rim, and the third with a low albedo spot. 3. The regolith particles are backscattering and carbon black is one of the few candidate regolith materials that might explain this low albedo. We conclude that Borrelly's surface is geologically complex to the limit of resolution of the images with a combination complex topography, pits, troughs, peaks and ridges, and some very dark albedo markings, perhaps a factor of two to three darker than the average 3-4% albedo of the surrounding terrains. Our technique utilizing measured radiance profiles through the dark regions is able to discriminate between rimmed depressions, rimless depressions and simple albedo changes not associated with topography. 相似文献
5.
Chandrasekhar T. Ashok N. M. Tej Anandamayee Mondal Soumen Watson P. V. 《Earth, Moon, and Planets》1998,81(2):111-121
During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J,
H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature
of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived
in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains
with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain
the unusual brightness of comet Hale—Bopp.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
We present results of a five-filter photometric study of Mercury's integral phase curve in the Johnson-Cousins UBVRI system, performed with the 0.90-m Westerlund Telescope in Uppsala, Sweden. CCD observations were made of the integrated disk for the phase angle range 22-152°, and the study is the first to cover the extended visible spectrum of Mercury. The observations are analyzed with Hapke's semi-empirical radiative transfer-based light-scattering model and photometric quantities are derived. A statistically significant phase reddening effect of is determined for Mercury based on color index observations, which is similar to that of the Moon. Phase coefficients fit to integral absolute magnitude data and Hapke models in combination with color index data provide a phase reddening effect of which does however not provide statistically significant evidence for its presence. Phase coefficients indicate that phase reddening may be decreasing in magnitude with wavelength. As for the case with the Moon, the value of the phase integral increases with wavelength, but at an eight times higher rate. This value is consistent with the difference in the rate of change in the spectral slope-emission angle relation for the two bodies. We attribute these differences with Mercury's redder spectral slope and an increase with wavelength of the backscattering lobe amplitude in the double Henyey-Greenstein particle phase function formulation. The normal albedo of integral Mercury at 1064 nm, pertinent to the return pulse energy of the BepiColombo laser altimeter (BELA), is estimated to 0.23±0.06 with a range of 0.13-0.33 for 99% of the surface. 相似文献
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利用一个考虑了辐射能传输的二维能量平衡气候模式,解析地分析了二氧化碳浓度改变后冰界纬度的变化,得到了冰界纬度随CO2浓度变化的关系以及全球平均温度的变化曲线.结果表明,当CO2浓度由工业革命前的280×10-6增加到700×10-6时,冰界仅后退(北半球向北)几个纬度;当CO2的浓度继续增加时,冰界纬度会加速向极地退缩,直至出现全球无极冰覆盖的现象.同样地,当CO2浓度由280×10-6增加到700×10-6时,全球地表平均温度虽然在增加,但增加的速率很小,并且增加的速率在减小,而当大于700×10-6之后,温度增加的速率会快速增大,温度将加速上升.对不同反照率进行敏感性试验,发现当反照率从0.1到0.32时,结果并没有显著地改变,即结果对反照率的变化并不敏感.这一计算结果表明,在目前的状态下,由CO2引起的增温作用似乎处于变化很小的准饱和状态,即目前气候不会因为CO2浓度的增加而迅速变暖.较为实际的情形可能是大气温度在缓慢增加到一定程度后才会迅速升高.这并不意味着可以忽视CO2的增温效应,因为根据计算结果,这个临界值大概在700×10-6左右,当CO2浓度增加到超过临界值之后,气温会剧烈上升,气候将会处在一个非常温暖的阶段. 相似文献
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用空间分辨率为１ｋｍ的ＭＯＤＩＳ和ＭＩＳＲ数据可计算１６天ＢＲＤＦ和反照率产品，该文证明了在多数采样条件下，用ＭＯＤＩＳ／ＭＩＳＲ角度采样的ＢＲＤＦ和反照率反演精度在５到１０个百分点以内。 相似文献