An algorithm using visible and 1.38-/spl mu/m channels to retrieve cirrus cloud reflectances from aircraft and satellite data

The Moderate Resolution Imaging Spectro-Radiometer (MODIS) on the Terra spacecraft has a channel near 1.38 /spl mu/m for remote sensing of high clouds from space. The implementation of this channel on MODIS was primarily based on previous analysis of hyperspectral imaging data collected with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). We describe an algorithm to retrieve cirrus bidirectional reflectance using channels near 0.66 and 1.38 /spl mu/m. It is shown that the apparent reflectance of the 1.38-/spl mu/m channel is essentially the bidirectional reflectance of cirrus clouds attenuated by the absorption of water vapor above cirrus clouds. A practical algorithm based on the scatterplot of 1.38-/spl mu/m channel apparent reflectance versus 0.66-/spl mu/m channel apparent reflectance has been developed to scale the effect of water vapor absorption so that the true cirrus reflectance in the visible spectral region can be obtained. To illustrate the applicability of the present algorithm, results for cirrus reflectance retrievals from AVIRIS and MODIS data are shown. The derived cirrus reflectance in the spectral region of 0.4-1 /spl mu/m can be used to remove cirrus contamination in a satellite image obtained at a visible channel. An example of such an application is shown. The spatially averaged cirrus reflectances derived from MODIS data can be used to establish global cirrus climatology, as is demonstrated by a sample global cirrus reflectance image.     

利用MODIS近红外陆地通道反演浑浊水体上空气溶胶光学厚度

目前MODIS海洋气溶胶反演算法能够很好地给出远海气溶胶性质,但近海结果并不理想。这是因为近海浑浊水体对0.55 µm、0.646 µm波段不能视为暗目标,对于0.86 µm波段也并不是总能视为暗目标。本研究采用MODIS近红外陆地通道对中国东南近海浑浊水体上空的气溶胶进行了反演研究,结果与AEROET符合得较好,这种算法可以很容易的与现行算法相结合,从而能够获得更多宝贵的气溶胶数据。     

A new concept on remote sensing of cirrus optical depth and effective ice particle size using strong water vapor absorption channels near 1.38 and 1.88 /spl mu/m

Techniques for retrieving cloud optical properties, i.e., the optical depths and particle size distributions, using atmospheric "window" channels in the visible and near-infrared spectral regions are well established. For partially transparent thin cirrus clouds, these "window" channels receive solar radiances scattered by the surface and lower level water clouds. Accurate retrieval of optical properties of thin cirrus clouds requires proper modeling of the effects from the surface and the lower level water clouds. In this paper, we describe a new concept using two strong water vapor absorption channels near 1.38 and 1.88 /spl mu/m, together with one window channel, for remote sensing of cirrus optical properties. Both the 1.38- and 1.88-/spl mu/m channels are highly sensitive in detecting the upper level cirrus clouds. Both channels receive little scattered solar radiances from the surface and lower level water clouds because of the strong water vapor absorption below cirrus. The 1.88-/spl mu/m channel is quite sensitive to changes in ice particle size distributions, while the 1.38-/spl mu/m channel is less sensitive. These properties allow for simultaneous retrievals of optical depths and particle size distributions of cirrus clouds with minimal contaminations from the surface and lower level water clouds. Preliminary tests of this new concept are made using hyperspectral imaging data collected with the Airborne Visible Infrared Imaging Spectrometer. The addition of a channel near 1.88 /spl mu/m to future multichannel meteorological satellite sensors would improve our ability in global remote sensing of cirrus optical properties.     

光谱响应函数和带宽对光学复杂二类水体离水辐射反射率的影响

在海洋水色遥感研究中,Ⅱ类水体由于具有复杂的光学属性并受多种物质的共同影响,会使水色遥感数据的应用水平和反演精度降低。从中分辨率成像光谱仪（Moderate Resolution Imaging Spectroradiometer, MODIS）和主题绘图仪（ThematicMapper,TM）光谱通道的光谱响应函数和带宽的角度出发,分析了其对光学复杂Ⅱ类水体离水辐射反射率的影响。结果表明,MODIS的光谱响应函数和带宽对离水辐射反射率的影响远小于TM相应通道对离水辐射反射率的影响。通过进一步定量分析发现,光谱响应函数和带宽在不同通道和水体下对离水辐射反射率的影响程度不同。针对长江河口三种不同的典型水体类型,利用TM通道的离水辐射反射率模拟了整个通道上的反射率。这样可以更明显地表征出通道内的水体光谱特性,消除光谱响应函数和带宽的影响。     

A technique for detecting burn scars using MODIS data

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the National Aeronautics and Space Administration Terra and Aqua spacecrafts have several visible and near-infrared (NIR) channels with resolutions of 250, 500, and 1 km for remote sensing of land surfaces and atmosphere. The MODIS data directly broadcasted to ground receiving stations can have many practical applications, including the rapid assessment of fires and burned areas. In this paper, we describe an empirical technique for remote sensing of burn scars using a single dataset of MODIS NIR channels centered near 1.24 and 2.13 /spl mu/m. These channels are sensitive to changes in the surface properties induced by the fire and are not obscured by smoke. Therefore, they allow remote sensing of burn scars in the presence of smoke. Detection of burn scars from single MODIS images, without the need of data from previous days, is very useful for near real-time burn scar recognition in operational direct broadcasting systems. The technique is applied to MODIS data acquired over the western U.S. during the summer fire season, the southeastern part of Canada during the summer and spring seasons, and the southeastern part of Australia. The burnt areas estimated from MODIS data are consistent with those estimated from the high spatial resolution Landsat 7 imaging data.     

Virtual sensors: using data mining techniques to efficiently estimate remote sensing spectra

Various instruments are used to create images of the earth and other objects in the universe in a diverse set of wavelength bands with the aim of understanding natural phenomena. Sometimes these instruments are built in a phased approach, with additional measurement capabilities added in later phases. In other cases, technology may mature to the point that the instrument offers new measurement capabilities that were not planned in the original design of the instrument. In still other cases, high-resolution spectral measurements may be too costly to perform on a large sample, and therefore, lower resolution spectral instruments are used to take the majority of measurements. Many applied science questions that are relevant to the earth science remote sensing community require analysis of enormous amounts of data that were generated by instruments with disparate measurement capabilities. This work addresses this problem using virtual sensors: a method that uses models trained on spectrally rich (high spectral resolution) data to "fill in" unmeasured spectral channels in spectrally poor (low spectral resolution) data. The models we use Are multilayer perceptrons, support vector machines (SVMs) with radial basis function kernels, and SVMs with mixture density Mercer kernels. We demonstrate this method by using models trained on the high spectral resolution Terra Moderate Resolution Imaging Spectrometer (MODIS) instrument to estimate what the equivalent of the MODIS 1.6-/spl mu/m channel would be for the National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (AVHRR/2) instrument. The scientific motivation for the simulation of the 1.6-/spl mu/m channel is to improve the ability of the AVHRR/2 sensor to detect clouds over snow and ice.     

Spatially complete global spectral surface albedos: value-added datasets derived from Terra MODIS land products

Recent production of land surface anisotropy, diffuse bihemispherical (white-sky) albedo, and direct-beam directional hemispherical (black-sky) albedo from observations acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the National Aeronautics and Space Administration's Terra and Aqua satellite platforms have provided researchers with unprecedented spatial, spectral, and temporal information on the land surface's radiative characteristics. Cloud cover, which curtails retrievals, and the presence of ephemeral and seasonal snow limit the snow-free data to approximately half the global land surfaces on an annual equal-angle basis. This precludes the MOD43B3 albedo products from being used in some remote sensing and ground-based applications, climate models, and global change research projects. An ecosystem-dependent temporal interpolation technique is described that has been developed to fill missing or seasonally snow-covered data in the official MOD43B3 albedo product. The method imposes pixel-level and local regional ecosystem-dependent phenological behavior onto retrieved pixel temporal data in such a way as to maintain pixel-level spatial and spectral detail and integrity. The phenological curves are derived from statistics based on the MODIS MOD12Q1 IGBP land cover classification product geolocated with the MOD43B3 data. The resulting snow-free value-added products provide the scientific community with spatially and temporally complete global white- and black-sky surface albedo maps and statistics. These products are stored on 1-min and coarser resolution equal-angle grids and are computed for the first seven MODIS wavelengths, ranging from 0.47-2.1 /spl mu/m and for three broadband wavelengths 0.3-0.7, 0.3-5.0, and 0.7-5.0 /spl mu/m.     

Retrievals of profiles of fine and coarse aerosols using lidar and radiometric space measurements

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) spaceborne lidar, expected to be launched in 2004, will collect profiles of the lidar attenuated backscattering coefficients of aerosol and clouds at 0.53 and 1.06 /spl mu/m. The measurements are sensitive to the vertical distribution of aerosols. However, the information is insufficient to be mapped into unique aerosol physical properties and vertical distribution. Spectral radiances measured by the Moderate Resolution Imaging Spectrometer (MODIS) on the Aqua spacecraft, acquired simultaneously with the CALIPSO observations, can constrain the solutions. The combination of the MODIS and CALIPSO data can be used to derive extinction profiles of the fine and coarse modes of the aerosol size distribution for aerosol optical thickness of 0.1 and larger. Here we describe a new inversion method developed to invert simultaneously MODIS and CALIPSO data over glint-free ocean. The method is applied to aircraft lidar and MODIS data collected over a dust storm off the coast of West Africa during the Saharan Dust Experiment (SHADE). The backscattering-to-extinction ratio (BER) (BER=/spl omega//sub o/P(180)/4/spl pi/) can be retrieved from the synergism between measurements avoiding a priori hypotheses required for inverting lidar measurements alone. For dust, the resultant value of BER =0.016 sr/sup -1/ is over 50% smaller than what is expected using Mie theory, but in good agreement with recent results obtained from Raman lidar observations of dust episodes. The inversion is robust in the presence of 10% and 20% noise in the lidar signal at 0.53 and 1.06 /spl mu/m, respectively. Calibration errors of the lidar of 5% to 10% can cause an error in optical thickness of 20% to 40%, respectively, in the tested cases.     

Effects of neglecting polarization on the MODIS aerosol retrieval over land

Reflectance measurements in the visible and infrared wavelengths, from the Moderate Resolution Imaging Spectroradiometer (MODIS), are used to derive aerosol optical thicknesses (AOTs) and aerosol properties over ocean and land surfaces, separately. Both algorithms employ radiative transfer (RT) code to create lookup tables, simulating the top-of-atmosphere (TOA) reflectance measured by the satellite. Whereas the algorithm over ocean uses a vector RT code that includes the effects of atmospheric polarization, the algorithm over land assumes scalar RT, thus neglecting polarization effects. In the red (0.66 /spl mu/m) and infrared (2.12 /spl mu/m) MODIS channels, scattering by molecules (Rayleigh scattering) is minimal. In these bands, the use of a scalar RT code is of sufficient accuracy to model TOA reflectance. However, in the blue (0.47 /spl mu/m), the presence of larger Rayleigh scattering (optical thickness approaching 0.2) results in nonnegligible polarization. The absolute difference between vector- and scalar-calculated TOA reflectance, even in the presence of depolarizing aerosols, is large enough to lead to substantial errors in retrieved AOT. Using RT code that allows for both vector and scalar calculations, we examine the reflectance differences at the TOA, assuming discrete loadings of continental-type aerosol. We find that the differences in blue channel TOA reflectance (vector-scalar) may be greater than 0.01 such that errors in derived AOT may be greater than 0.1. Errors may be positive or negative, depending on the specific geometry, and tend to cancel out when averages over a large enough sample of satellite geometry. Thus, the neglect of polarization introduces little error into global and long-term averages, yet can produce very large errors on smaller scales and individual retrievals. As a result of this study, a future version of aerosol retrieval from MODIS over land will include polarization within the atmosphere.     

多种卫星传感器反演长江口悬浮泥沙浓度的对比分析

通过用Shen等~([1])的方法对Terra/MODIS、FY-3A/MERSI、COMS/GOCI传感器入瞳处的辐射亮度即天顶辐射亮度进行反演计算,得出了遥感反射率Rrs与悬浮颗粒物(Suspended Particulate Matter,SPM)浓度的数据,并将上述反演与Envisat/MERIS反演进行了对比。结果表明,MODIS、MERSI、GOCI传感器的天顶辐射亮度与MERIS的线性相关性均较好;GOCI、MODIS与MERIS的Rrs一致,MERSI与MERIS的R_(rs)相差较大,尤其在近红外区域。MODIS、MERSI和GOCI反演的SPM数据与MERIS反演的绝对偏差分别为36%、31%和26%。对于长江口、杭州湾及江苏沿岸的高浊度水体,3种传感器反演的SPM均与MERIS反演的SPM相近。对于离岸较远的低浊度水体,仅GOCI能很好地体现。     

Emissivity maps to retrieve land-surface temperature from MSG/SEVIRI

Retrieval of land-surface temperature (LST) using data from the METEOSAT Second Generation-1 (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) requires adequate estimates of land-surface emissivity (LSE). In this context, LSE maps for SEVIRI channels IR3.9, IR8.7, IR10.8, and IR12.0 were developed based on the vegetation cover method. A broadband LSE map (3-14 /spl mu/m) was also developed for estimating longwave surface fluxes that may prove to be useful in both energy balance and climate modeling studies. LSE is estimated from conventional static land-cover classifications, LSE spectral data for each land cover, and fractional vegetation cover (FVC) information. Both International Geosphere-Biosphere Program (IGBP) Data and Information System (DIS) and Moderate Resolution Imaging Spectrometer (MODIS) MOD12Q1 land-cover products were used to build the LSE maps. Data on LSE were obtained from the Johns Hopkins University and Jet Propulsion Laboratory spectral libraries included in the Advanced Spaceborne Thermal Emission and Reflection Radiometer spectral library, as well as from the MODIS University of California-Santa Barbara spectral library. FVC data for each pixel were derived based on the normalized differential vegetation index. Depending on land cover, the LSE errors for channels IR3.9 and IR8.7 spatially vary from /spl plusmn/0.6% to /spl plusmn/24% and /spl plusmn/0.1% to /spl plusmn/33%, respectively, whereas the broadband spectrum errors lie between /spl plusmn/0.3% and /spl plusmn/7%. In the case of channels IR10.8 and IR12.0, 73% of the land surfaces within the MSG disk present relative errors less than /spl plusmn/1.5%, and almost all (26%) of the remaining areas have relative errors of /spl plusmn/2.0%. Developed LSE maps provide a first estimate of the ranges of LSE in SEVIRI channels for each surface type, and obtained results may be used to assess the sensitivity of algorithms where an a priori knowledge of LSE is required.     

Terra MODIS on-orbit spectral characterization and performance

The Moderate Resolution Imaging Spectroradiometer (MODIS) protoflight model onboard the National Aeronautics and Space Administration's Earth Observing System Terra spacecraft has been in operation for over five years since its launch in December 1999. It makes measurements using 36 spectral bands with wavelengths from 0.41 to 14.5 /spl mu/m. Bands 1-19 and 26 with wavelengths below 2.2 /spl mu/m, the reflective solar bands (RSBs), collect daytime reflected solar radiance at three nadir spatial resolutions: 0.25 km (bands 1-2), 0.5 km (bands 3-7), and 1 km (bands 8-19 and 26). Bands 20-25 and 27-36, the thermal emissive bands, collect both daytime and nighttime thermal emissions, at 1-km nadir spatial resolution. The MODIS spectral characterization was performed prelaunch at the system level. One of the MODIS onboard calibrators, the Spectroradiometric Calibration Assembly (SRCA), was designed to perform on-orbit spectral characterization of the MODIS RSB. This paper provides a brief overview of MODIS prelaunch spectral characterization, but focuses primarily on the algorithms and results of using the SRCA for on-orbit spectral characterization. Discussions are provided on the RSB center wavelength measurements and their relative spectral response retrievals, comparisons of on-orbit results with those from prelaunch measurements, and the dependence of center wavelength shifts on instrument temperature. For Terra MODIS, the center wavelength shifts over the past five years are less than 0.5 nm for most RSBs, indicating excellent stability of the instrument's spectral characteristics. Similar spectral performance has also been obtained from the Aqua MODIS (launched in May 2002) SRCA measurements.     

Arctic sea ice, cloud, water, and lead classification using neural networks and 1.6-/spl mu/m data

Polar sea ice plays a critical role in regulating the global climate. Seasonal variation in sea ice extent, however, coupled with the difficulties associated with in situ observations of polar sea ice, makes remote sensing the only practical way to estimate this important climatic variable on the space and time scales required. Unfortunately, accurate retrieval of sea ice extent from satellite data is a difficult task. Sea ice and high cold clouds have similar visible reflectance, but some other types of clouds can appear darker than sea ice. Moreover, strong atmospheric inversions and isothermal structures, both common in winter at some polar locations, further complicate the classification. This paper uses a combination of feed-forward neural networks and 1.6-/spl mu/m data from the new Chinese Fengyun-1C satellite to mitigate these difficulties. The 1.6-/spl mu/m data are especially useful for detecting illuminated water clouds in polar regions because 1) at 1.6 /spl mu/m, the reflectance of water droplets is significantly higher than that of snow or ice and 2) 1.6-/spl mu/m data are unaffected by atmospheric inversions. Validation data confirm the accuracy of the new classification technique. Application to other sensors with 1.6-/spl mu/m capabilities also is discussed.     

Implementation of both high-hole and electron mobility in strained Si/strained Si/sub 1-y/Ge/sub y/ on relaxed Si/sub 1-x/Ge/sub x/ (x

Jongwan Jung Lee  M.L. Shaofeng Yu Fitzgerald  E.A. Antoniadis  D.A. 《Electron Device Letters, IEEE》2003,24(7):460-462

可见-红外宽光谱的两种分色方法

空间光学遥感仪器的工作光谱往往覆盖从可见到长波红外的宽光谱范围,它们是利用数个甚至二十多个光谱通道获取信息的.因此通常需要一个覆盖全光谱的分色片将光谱一分为二,将不同光谱分配到透射和反射光路中.通过对基片材料、膜层材料、膜系结构的设计和分析,得到可见-红外宽光谱的两种分色方法.利用真空中的光学薄膜沉积技术,制备出了两类性能良好的可见-红外宽光谱分色片,光谱覆盖范围0.4μm～13μm,可见光区透射率大于80%,6μm ～13μm的长波红外反射率大于90%.     

Characteristics of a photonic crystal defect waveguide-coupled quantum-dot photodiode

We have investigated the characteristics of an In/sub 0.4/Ga/sub 0.6/As self-organized quantum-dot (QD) resonant-cavity photodiode. The QD epitaxy and the design of the two-dimensional photonic crystal cavity are tailored for 1.3-/spl mu/m wavelength operation. The input excitation to the photodiode is provided with an in-plane defect waveguide designed with the same photonic crystal. The measured spectral photocurrent characteristics reflect mode coupling between the waveguide and detector and the resonant cavity effect due to total internal reflection and photonic bandgap confinement. The photocurrent response is explained with a model involving the circulating fields in the cavity. The characteristics are also dependent of cavity size. Enhancement and narrowing (/spl sim/ 10 nm) of the photoresponse at /spl lambda//spl sim/1.3 /spl mu/m are observed. A spectral dip, of /spl sim/ 10-nm width, also observed at 1.3 /spl mu/m is possibly due to the anticrossing mechanism, uniquely present in photonic crystal waveguides.     

Polarization independent bulk active region semiconductor optical amplifiers for 1.3 /spl mu/m wavelengths

Semiconductor optical amplifiers for 1.3 /spl mu/m are realized combining single-step grown bulk InGaAsP active region with ridge-waveguides. Achieved fiber-to-fiber gains are in excess of 27 dB with spectral ripples below 0.2 dB. Gain is polarization insensitive to within 1 dB over the entire range of driving current, 1.28 /spl mu/m to 1.34 /spl mu/m wavelength and 10/spl deg/C to 50/spl deg/C heat sink temperature. Intrinsic noise figure is 6.3 dB. Gain saturates at +10 dBm.     

AIRS/Vis near IR instrument

A component of the Atmospheric Infrared Sounder (AIRS) instrument system is the AIRS/Visible Near InfraRed (Vis/NIR) instrument. With a nadir ground resolution of 2.28 km and four channels, the Vis/NIR instrument provides diagnostic support to the infrared retrievals from the AIRS instrument and several research products, including surface solar flux studies. The AIRS Vis/NIR is composed of three narrowband (channel 1: 0.40-0.44 /spl mu/m; channel 2: 0.58-0.68 /spl mu/m, and channel 3: 0.71-0.92 /spl mu/m) and one broadband (channel 4: 0.49-0.94 /spl mu/m) channel, each a linear detector array of nine pixels. It is calibrated onboard with three tungsten lamps. Vicarious calibrations using ground targets of known reflectance and a cross-calibration with the Moderate Resolution Imaging Spectroradiometer (MODIS) augment the onboard calibration. One of AIRS Vis/NIR's principal supporting functions is the detection of low clouds to flag these conditions for atmospheric temperature retrievals. Once clouds are detected, a cloud height index is obtained based on the ratio (channel 2 - channel 3)/channel 1 that is sensitive to the partitioning of water vapor absorption above and below clouds. The determination of the surface solar radiation flux is principally based on channel 4 broadband measurements and the well-established relationship between top-of-the atmosphere (broadband) radiance and the surface irradiance.     

An autonomous above-water system for the validation of ocean color radiance data

An operational system for autonomous above-water radiance measurements, called the SeaWiFS Photometer Revision for Incident Surface Measurements (SeaPRISM), was deployed at the Acqua Alta Oceanographic Tower in the northern Adriatic Sea and used for the validation of remote sensing radiometric products in coastal waters. The SeaPRISM data were compared with simultaneous data collected from an independent in-water system for a wide variety of sun elevations along with different atmospheric, seawater, and sea state conditions. The average absolute differences between the above- and in-water determinations of water-leaving radiances (computed linearly) were less than 4.5% in the 412-555-nm spectral interval. A similar comparison for normalized water-leaving radiances showed average absolute differences less than 5.1%. The comparison between normalized water-leaving radiances computed from remote sensing and SeaPRISM matchup data, showed absolute spectral average (linear) differences of 17.0%, 22.1%, and 20.8% for SeaWiFS, MODIS, and MERIS, respectively. The results, in keeping with those produced by independent in-water systems, suggest the feasibility of operational coastal networks of autonomous above-water radiometers deployed on fixed platforms (towers, lighthouses, navigation aids, etc.) to support ocean color validation activities.