Spectral Adjustment Research Articles

Determination of spallation neutron flux through spectral adjustment techniques

The Los Alamos Isotope Production Facility (IPF) creates medical isotopes using a proton beam impinged on a target stack. Spallation neutrons are created in the interaction of the beam with target. The use of these spallation neutrons to produce additional radionuclides has been proposed. However, the energy distribution and magnitude of the flux is not well understood. A modified SAND-II spectral adjustment routine has been used with radioactivation foils to determine the differential neutron fluence for these spallation neutrons during a standard IPF production run.

A Web-Based Tool for Calculating Spectral Band Difference Adjustment Factors Derived From SCIAMACHY Hyperspectral Data

Monitoring and adjusting calibrations of various satellite imagers is often exacerbated by differences in their spectral response functions (SRFs). To help account for spectral disparities among satellite imagers, a web-based spectral band difference correction calculator has been developed to characterize the relationship between a specified pair of satellite imager channels in the hyperspectral wavelength range of 240-1750 nm. These spectral band adjustment factors (SBAFs) are derived by convolving hyperspectral data from the SCIAMACHY instrument with the SRFs of a reference and target sensor. The SBAF tool can be used for all combinations of instrument/channel pairs over predefined Earth spectra, intercalibration domains, or user-defined spatial domains. Options are available to the user whereby SBAFs can be subsetted by time, angle, and/or precipitable water content. To evaluate the relative spectral calibration of SCIAMACHY, comparisons of SBAFs derived from SCIAMACHY, Hyperion, and Global Ozone Monitoring Experiment-2 (GOME-2) were performed. Using observations over the Libya 4 desert pseudoinvariant calibration site, it is shown that SCIAMACHY-based SBAFs are within 0.1%-0.3% of SBAFs derived from Hyperion or GOME-2. This result implies that spectral calibration differences, i.e., the calibration uncertainties of SCIAMACHY relative to other potential spectral sources, have a minor impact on the SBAF compared with the influence of effective parameter-based subsetting. The SCIAMACHY instrument is most suited for calculating the SBAFs, given its high spectral resolution, broad spectral range, and nearly continuous global availability. The calibration community will find this SBAF tool useful for mitigating the SRF differences that can complicate the comparison and intercalibration of visible and near-infrared sensors.

An Arrayed Liquid Crystal Fabry–Perot Infrared Filter for Electrically Tunable Spectral Imaging Detection

An arrayed electrically tunable infrared (IR) filter based on the key structure of liquid crystal Fabry–Perot (LC-FP) working in the wavelength range from 2.5 to $5~\mu \text{m}$ is designed and fabricated successfully. According to the electrically controlled birefringence characteristics of nematic LC molecules, the refractive index of LC materials filled into a prefabricated microcavity can be adjusted by the spatial electric field stimulated between the top and bottom aluminum (Al) electrodes. As a crucial component of the filter, the Al film with a typical thickness of $\sim 30$ nm acts as the electrode as well as the reflective mirror. The particular functions, including key spectral selection and spectral adjustment, can be realized by the developed LC-FP filter driven electrically. Our experiments show that the maximum transmittance of the transmission peaks is $\sim 24$ %, and the transmission spectrum can be shifted remarkably through applying different voltage signals with a root mean square value range from 0 to $\sim 21.7~\text{V}_{\mathrm{ rms}}$ . The experimental results are consistent with the simulation according to the model constructed by us. As a $2 \times 2$ or four-channel IR filter, the top electrode of the device is composed of four same sub-electrodes. Each channel in the device is powered separately and synchronously to select desired transmission spectrum, which means that the device can be used to obtain spectral sub-images in different spectral bands in one shot.

Validation of the Calibration Coefficient of the GaoFen-1 PMS Sensor Using the Landsat 8 OLI

The panchromatic and multispectral (PMS) sensor is an optical imaging sensor aboard the Gao Fen-1 (GF-1) satellite. This work describes an approach to validate the calibration coefficients of the PMS sensors based on the image data of the Landsat 8 Operational Land Imager (OLI). Two image pairs, one obtained over the Dunhuang test site and the other over the Golmud test site, were used in this paper. Two spectral band adjustment factors (SBAF), given as the radiance SBAF and reflectance SBAF, were applied to correct the differences in the respective images caused by the relative spectral responses of the PMS sensor and OLI. Uncertainties in the SBAF values arising from atmospheric parameters and the absence of a measured ground spectrum were analyzed in this paper. The results show that the average relative differences of top-of-atmosphere radiance and reflectance values for each band between the PMS sensor and OLI images are 2%–5% for most bands, after SBAF correction with a measured ground spectrum or fitted spectrum. It is demonstrated that the OLI image can be used to validate the calibration coefficient of the PMS sensor, even if the image pairs are not imaged on the same day.

Least-Squares Neutron Spectral Adjustment with STAYSL PNNL

The STAYSL PNNL computer code, a descendant of the STAY'SL code [1], performs neutron spectral adjustment of a starting neutron spectrum, applying a least squares method to determine adjustments based on saturated activation rates, neutron cross sections from evaluated nuclear data libraries, and all associated covariances. STAYSL PNNL is provided as part of a comprehensive suite of programs [2], where additional tools in the suite are used for assembling a set of nuclear data libraries and determining all required corrections to the measured data to determine saturated activation rates. Neutron cross section and covariance data are taken from the International Reactor Dosimetry File (IRDF-2002) [3], which was sponsored by the International Atomic Energy Agency (IAEA), though work is planned to update to data from the IAEA's International Reactor Dosimetry and Fusion File (IRDFF) [4]. The nuclear data and associated covariances are extracted from IRDF-2002 using the third-party NJOY99 computer code [5]. The NJpp translation code converts the extracted data into a library data array format suitable for use as input to STAYSL PNNL. The software suite also includes three utilities to calculate corrections to measured activation rates. Neutron self-shielding corrections are calculated as a function of neutron energy with the SHIELD code and are applied to the group cross sections prior to spectral adjustment, thus making the corrections independent of the neutron spectrum. The SigPhi Calculator is a Microsoft Excel spreadsheet used for calculating saturated activation rates from raw gamma activities by applying corrections for gamma self-absorption, neutron burn-up, and the irradiation history. Gamma self-absorption and neutron burn-up corrections are calculated (iteratively in the case of the burn-up) within the SigPhi Calculator spreadsheet. The irradiation history corrections are calculated using the BCF computer code and are inserted into the SigPhi Calculator workbook for use in correcting the measured activities. Output from the SigPhi Calculator is automatically produced, and consists of a portion of the STAYSL PNNL input file data that is required to run the spectral adjustment calculations. Within STAYSL PNNL, the least-squares process is performed in one step, without iteration, and provides rapid results on PC platforms. STAYSL PNNL creates multiple output files with tabulated results, data suitable for plotting, and data formatted for use in subsequent radiation damage calculations using the SPECTER computer code (which is not included in the STAYSL PNNL suite). All components of the software suite have undergone extensive testing and validation prior to release and test cases are provided with the package.

On-Site Quality Control of Processed Land Animal Proteins Using a Portable Micro-Electro-Mechanical-Systems near Infrared Spectrometer

This study was carried out using a spectral database comprising 1164 samples of processed land animal proteins provided by a rendering plant located in southern Spain (Seville). A variety of cloning algorithms and strategies were evaluated for the transfer of spectroscopic databases obtained on a FOSS NIRSystems monochromator (FNS), currently in use for at-line NIR analysis in the rendering-industry laboratory, to a MicroPhazir Rx portable micro-electro-mechanical-systems (MEMS)-based NIR spectrometer. Application of the spectral difference by wavelengths algorithm for spectral adjustment using a 10-sample standardisation set enabled standardisation of the two instruments and effective transfer of spectral data: spectral concordance values, as estimated by the RMS(c) statistic, were very similar at 10,829 and 10,388 μlog (1/ R) for the master (MEMS-NIR) and satellite instruments (FNS), respectively. Once the database had been transferred to the master, calibration equations were developed to predict moisture, crude protein, ash, crude fat, fat after hydrolysis, digestible protein, Ca and P, with a view to comparing the predictive ability of these equations with that of equations obtained using the satellite. Equations developed in the two instruments displayed similar accuracy and precision.

분광 조정과 비등방성 확산에 의한 PAN-Sharpened 영상의 분광 왜곡 완화

This paper proposes a scheme to reduce spectral distortion in PAN-sharpening which produces a MultiSpectral image (MS) with the higher resolution of PANchromatic image (PAN). The spectral distortion results from reconstructing spatial details of PAN image in the MS image. The proposed method employs Spectral Adjustment and Anisotropic Diffusion to make a reduction of the distortion. The spectral adjustment makes the PAN-sharpened image agree with the original MS image, but causes block distortion because the spectral response of a pixel in the lower resolution is assumed to be equal to the average response of the pixels belonging to the corresponding area in the higher resolution at a same wavelength. The block distortion is corrected by the anisotropic diffusion which uses a conduct coefficient estimating from a local computation of PAN image. It results in yielding a PAN-sharpened image with the spatial structure of PAN image. GSA is one of PAN-sharpening techniques which are efficient in computation as well as good in quantitative quality evaluation. This study suggests the GSA as a preliminary PAN-sharpening method. Two data sets were used in the experiment to evaluate the proposed scheme. One is a Dubaisat-2 image of observed at Los Angeles area, USA on February, 2014, the other is an IKONOS of observed at Anyang, Korea on March, 2002. The experimental results show that the proposed scheme yields the PAN-sharpened images which have much less spectral distortion and better quantitative quality evaluation.

Evaluation of the Landsat-5 TM and Landsat-7 ETM+ surface reflectance products

Abstract Maintaining consistent datasets of Surface Reflectance (SR) is an important challenge to ensure long-term quality of Climate Data Records. The Landsat 5 and 7 archives offer a unique data source to monitor globally the land surface at high spatial resolution. The Landsat-5 TM and Landsat-7 ETM + SR products, derived from the on-demand processing Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS), require periodic evaluation to check the data consistency. Two evaluation approaches are presented in this paper. The first approach used the Aerosol Robotic Network (AERONET) data set for the period 2000 to 2013 over 489 sites with 3600 Landsat-5 TM and Landsat-7 ETM + scenes selected. For each scene, 10 × 10 km subsets of LEDAPS-derived Landsat SR and AERONET-derived SR are compared. The latter are computed using Landsat top of atmosphere reflectance, AERONET measurements of atmospheric parameters, and the 6S radiative transfer model. Second, we introduce a methodology to cross-compare Landsat data and MODIS data acquired on the same day. The analysis is based on 4000 random Landsat scenes globally distributed from 2000 to 2013. This method includes: (i) a surface anisotropy adjustment, based on the VJB Bidirectional Reflectance Distribution Function (BRDF) method, to adjust Terra and Aqua MODIS data to Landsat 5 and 7 sun-view geometry, (ii) a spectral adjustment based on an artificial neural network trained with the PROSAIL vegetation radiative transfer model, to adjust MODIS data to TM and ETM + spectral responses. The overall results of both approaches show a good match in over 80% of the scenes, i.e. the TM and ETM + SR uncertainty remained within the SR specification, defined as 0.05 × SR + 0.005. The worst results are found in the blue band used in LEDAPS to adjust the Aerosol Optical Thickness (AOT). The MODIS-Landsat SR cross-comparison confirms the utility of a BRDF adjustment method to decrease the scattering between Landsat sensors and MODIS sensors (Terra and Aqua). The spectral adjustment removes part of the biases related to spectral response differences. Global analysis is used to identify AOT retrieval issues over specific scenes, mostly over bright surfaces. From 2000 to 2013, no significant temporal variation of the performance is detected, which enhanced the consistency of LEDAPS-derived surface reflectance data set.

Cross-Calibration of the HSI Sensor Reflective Solar Bands Using Hyperion Data

This paper describes a methodology that uses Hyperion imagery as reference data to calibrate the Chinese Hyperspectral Imager (HSI) onboard the HJ-1A satellite. Two test sites near Dunhuang in Gansu and in Inner Mongolia were used for the cross-calibration. To account for the uncertainties in the top of atmosphere (TOA) reflectance due to the bidirectional reflectance distribution function (BRDF) and relative spectral response (RSR) differences between the two sensors, a model is adopted to transfer the Hyperion TOA reflectance to the effective HSI TOA reflectance. The influence of BRDF is analyzed, and two BRDF correction approaches are applied to the two test sites, respectively. For the Dunhuang test site, the ground synchronously measured reflectance in different solar zenith angles is used for BRDF correction. For the Inner Mongolia test site, a kernel-driven model is applied. The influence of RSR mismatch is computed using a spectral profile adjustment factor (SPAF), which takes into account the spectral profile of the target and the RSR of each sensor. The SPAF is calculated according to the TOA reflectance simulated using moderate resolution atmospheric transmission. One-point calibration and multipoint calibration coefficients are computed, respectively. Ground reflectance data measured in June 2010 at the Inner Mongolia test site were used to validate the cross-calibration coefficients based on the Hyperion image. The results support the proposal that the cross-calibration method between two hyperspectral sensors is effective, and the use of multipoint calibration coefficient with nonzero offset has great potential for hyperspectral sensor calibration.

Investigation of the dual-wavelength light-emitting diodes with AlInGaN spectral adjustment layer based on the Al/In ratios

In this paper, we propose AlxInyGazN quaternary alloys spectral adjustment layer (SAL) for visible spectrum control of dual-wavelength emission in single-chip InGaN/AlInGaN multiple quantum wells (MQWs) light-emitting diodes (LEDs). The mechanism and effects for visible spectrum control with different ratios of Al to In (Al/In) in the AlInGaN spectral adjustment layer are investigated numerically. With the increasing of the Al/In ratios in the spectral adjustment layer, the spontaneous emission rate of In0.08Ga0.92N/Al0.1In0.008Ga0.892N active region increase, while the spontaneous emission rate In0.16Ga0.84N/Al0.1In0.008Ga0.892N active region is suppressed. Besides, the influence of driving current for visible spectrum control is also expounded. The simulation results show that the spontaneous emission rate of In0.16Ga0.84N/Al0.1In0.008Ga0.892N active region could be enhanced more than In0.08Ga0.92N/Al0.1In0.008Ga0.892N active region with the increasing of driving current. By the adjustment of spontaneous rates in the two active regions, the relative luminous spectrum of dual-wavelength in InGaN/AlInGaN LEDs can be controlled.

MWIR/LWIR filter based on Liquid–Crystal Fabry–Perot structure for tunable spectral imaging detection

An electrically tunable medium-wave infrared (MWIR)/long-wave infrared (LWIR) filter based on the key structure of Liquid–Crystal (LC) Fabry–Perot (FP), which works in the wavelength range from 2.5μm to 12μm, is designed and fabricated successfully in this paper. According to the optical interference principle of the FP cavity and electrically controlled birefringence of nematic LC molecules, the particular functions including spectral selection and spectral staring and spectral adjustment, can be realized by the developed MWIR/LWIR filter driven and controlled electrically. As to the LC-FP filter, both planar reflective mirrors are shaped by depositing a layer of aluminum (Al) film (∼60nm) over one side of double-side polished Zinc Selenide (ZnSe) wafer (∼1mm), and then polyimide (PI) layer with the thickness of ∼100nm is coated directly on Al film. With typical sandwich architecture, the depth of the cavity with nematic LC molecules sealed in is ∼7.5μm. To make sure the LC molecules parallel aligned and twist regularly under voltage driving signal applied on Al film, which also acts as electrode, the V-grooves are formed in PI layer with the depth of ∼90nm and the width of ∼350nm at average by strong rubbing. The typical transmission spectrum in MWIR&LWIR wavelength range and several spectral images in MWIR wavelength range based on the fabricated LC-FP filter, have been obtained through applying a voltage driving-signal with different root-means-square (RMS) value over the electrodes of LC-FP filter in the selected voltage range from 0VRMS to 19.8VRMS. The testing result demonstrates a prospect of realization smart spectral imaging and further integrating the LC-FP filter with infrared focal plane arrays (FPAs) to achieve the purpose infrared multispectral imaging. The developed MWIR&LWIR LC-FP filters show some obvious advantages such as wide working wavelength range, electrically tunable spectral selection, ultra-compact, low cost, being compatible with standard microelectronic technology.

Intercalibration of GOES Imager visible channels over the Sonoran Desert

AbstractThe Geostationary Operational Environmental Satellites (GOES) have been observing the Western Hemisphere since the late 1970s, providing valuable information for weather forecast and climate change studies. Due to the lack of an onboard calibration device for the visible channel, accurate reflectance of the visible channel data depends on vicarious calibration methods to provide postlaunch calibration coefficients to compensate for the degraded responsivity. In this study, the Sonoran Desert, which can be viewed by both GOES‐East and GOES‐West satellites, is used to intercalibrate the visible channels on board the three‐axis stabilized GOES satellite Imagers traceable to the Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 (C6) calibration standard. It was found that when the anomalous reflectance in 2004 and 2005 are excluded, the Sonoran Desert is radiometrically, spatially, and spectrally stable at the GOES viewing geometries and thus can be considered as a pseudo‐invariant calibration site to develop long‐term GOES Imager visible data set. To characterize the desert target reflectance with the MODIS data, GOES observations over 1 year period are used to convert the MODIS reflectance to the GOES viewing and solar illumination geometries. The spectral band adjustment factor for each GOES Imager visible channel is generated with a set of clear‐sky Hyperion measurements. A trending algorithm, which consists of a polynomial function for the description of instrument degradation performance and two sine terms for the impacts of the seasonal variations of the solar zenith angle and atmospheric components, is applied to fit the time series of prelaunch calibrated reflectance. The combined calibration uncertainty of the desert calibration method is less than 4% at the Aqua MODIS C6 calibration standard. The difference of the postlaunch calibration coefficients between the desert calibration and the current GOES visible operational calibration methods is mainly within 5%.

Desert-Based Absolute Calibration of Successive Geostationary Visible Sensors Using a Daily Exoatmospheric Radiance Model

A desert daily exoatmospheric radiance model (DERM) based on a well-calibrated (reference) geostationary Earth orbit (GEO) satellite visible sensor can be used to transfer the calibration to a (target) GEO sensor located at the same equatorial longitude location. The DERM is based on the reference GEO daily radiances observed over a single pseudoinvariant calibration site (PICS) being that the daily angular conditions are repeated annually for any historical or successive colocated GEO. The GEO-specific PICSs used in the study are first inspected using the well-calibrated Aqua-MODerate Resolution Imaging Spectroradiometer (MODIS) exoatmospheric reflectances for stability. The Libyan Desert site was found to be stable within 1 % over ten years. The average clear-sky daily local-noon interannual variability based on Meteosat-9 0.65- μm top-of-atmosphere radiances over the Libyan Desert is 0.74 %, which implies that the combined surface and atmospheric column is invariant. A spectral band adjustment factor, based on Scanning Imaging Absorption Spectrometer for Atmospheric Cartography spectral radiances, is used to account for sensor spectral response function (SRF) differences between the reference and target GEO. The GEO reference calibration was based on the GEO/Aqua-MODIS ray-matched radiance intercalibration transfer technique. The reference Meteosat-9 DERM and ray-matched calibration consistency was within 0.4 % and 1.9 % for Meteosat-8 and Meteosat-7, respectively. Similarly, GOES-10 and GOES-15 were calibrated based on the GOES-11 DERM using the Sonoran Desert and were found to have a consistency within 1 % and 3 %, respectively.

Post calibration of channels 1 and 2 of long-term AVHRR data record based on SeaWiFS data and pseudo-invariant targets

Advanced very high resolution radiometer (AVHRR) data provide a global, long-term, consistent time series with favorable spectral and spatial resolution. Such measurements are necessary for climate change studies. However, significant problems with the AVHRR calibration have been seen in two separate sources of early AVHRR data — lack onboard calibration and observed trends and biases when the AVHRR radiances are compared with other accurate top-of-atmosphere (TOA) radiances sources. In this paper, new calibration coefficients for channels 1 and 2 of the AVHRR sensors onboard 16 NOAA satellites from TIROS-N, NOAA-6 to NOAA-19, and Metop-A, B are reported. The calibration slopes are derived based on several pseudo-invariant sites endorsed by the Committee on Earth Observation Satellites (CEOS). Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) channels 6 and 8 radiance data are applied in characterizing the bidirectional reflectance distribution functions (BRDF) of the TOA reflectance over the employed targets, and MODTRAN simulations are carried out to parameterize the spectral channel adjustment factors (SBAFs) between SeaWiFS and each AVHRR sensor to eliminate the spectral response differences over different targets considering the impacts of observing geometries and gaseous absorption. The BRDFs and SBAFs are then applied to filtered AVHRR time-series to generate time series of calibration slopes presented in the form of quadratic polynomials as a function of time and applied in the recalibration of AVHRR data records. Comparisons with calibration coefficients generated from other products exhibit preferable validity and consistency, and notable incoherence and trend in the TOA reflectance time series of the L1B AVHRR data over each site from all the launched NOAA series polar orbiting satellites are largely eliminated after the recalibration. The long-term and inter-sensor consistent AVHRR data records after this post calibration can provide valuable insight into global climate changes since 1978.

基于多光源的光谱分布可调谐光源系统

A spectrum-tunable integrating sphere light source based on a Light Emitting diode (LED) and basis sources was developed to eliminate the effect of spectral non-matching between calibration source and an on-orbit detecting target on the calibration accuracy of space optical remote sensor in a laboratory. The developed source was used to produce typical ground object spectra and to calibrate space optical remote sensors, which significantly diminishes the absolute radiometric calibration error caused by spectral non-matching mentioned above. Firstly, the affecting mechanism of the spectral non-matching on the absolute radiometric calibration accuracy of space optical remote sensor was analyzed. Then, the design scheme of the spectrum-tunable light source was given according to technical requirements. The scheme was mainly divided into four key issues: the determination of light source and design of spectral matching algorithm, the design of light source drive circuit and control system, the matching of target spectrum and spectral adjustment, and the optical-mechanical design of spectrum-tunable light source. In the end, the performance of calibrated spectrum-tunable light source was tested. The results show that the spectral non-matching errors of equi-energy spectrum and 6000 K blackbody spectrum are 6.37% and 8.76% respectively, the irradiance non-uniformity is 0.53%, the irradiance instability of the spectrum-tunable light source within 30 min is 0.03%, and the radiance angular non-uniformity of the spectrum-tunable light source within horizontally 30 is 0.80%. Moreover, it offers the spectral radiance above 0.07 W/(m2srnm) and the integral radiance in 410-900 nm of 58.3 W/(m2sr). These data all meet the design requirements of spectrum-tunable light sources.

Characterization of a Thermo Scientific D711 D-T neutron generator located in a low-scatter facility

A dosimetry experiment used to measure the neutron flux and spectrum of a D-T neutron generator is presented. The D-T generator at Pacific Northwest National Laboratory is installed in the middle of a large room to minimize scatter of neutrons back to the sample. The efficacy of maintaining a pure fast neutron field for the sample is investigated. Twenty-one positions within 13cm of the neutron source contained foils or wires of Fe, Ni, and Al with additional Au, and in monitors at some locations. Spectral adjustment of the neutron flux at each position based on the measured reaction rates and theoretical Monte Carlo calculations show that at least 99.1% of the spectrum lies above 110keV for all measured positions, and neutrons above 14MeV can account for as much as 91% at locations along the axis of the generator and close to the source. The 14MeV component drops to 77% in radial positions far from the source. The largest total flux observed was 8.29E+08n/cm2s (±1.4%) in the center of the cooling cap, although additional experiments have shown this value could be as high as 1.20E+09n/cm2s.

A simplified analysis of dimethylarsinic acid by wavelength dispersive X-ray fluorescence spectrometry combined with a strong cation exchange disk

Dimethylarsinic acid (DMAV) was pre-concentrated from water samples using a strong cation exchange (SCX) disk functionalized with sulfonic groups, before being analyzed by wavelength dispersive X-ray fluorescence spectrometry (WDXRF). The adsorption of DMAV occurred preferentially on the surface of the SCX disk, regardless of pH levels, probably due to interactions with the sulfonic functional groups. However, no other arsenic species, such as arsenate (iAsV), arsenite (iAsIII), and monomethylarsonic acid (MMAV), were retained. The SCX-WDXRF method produced a strongly linear calibration curve (R2=0.9996) with its limit of detection at 0.218μgL−1 when a one-liter water sample was used for pre-concentration. The As intensity of the system was sensitive to the Pb content retained on the SCX disk owing to the proximity of the As-Kα and Pb-Lα lines. To compensate for this interference, a correction factor was developed by considering the calibration slope ratio between the X-ray intensity measured at a Bragg angle of 48.781° and the Pb content of the SCX disks. The results of spike tests for iAsV, iAsIII, MMAV, and DMAV with and without the addition of Pb in synthetic landfill leachate exhibited reasonable recoveries (i.e., 98–105%) after the spectral adjustment for the Pb interference.

Songs of the city: noise-dependent spectral plasticity in the acoustic phenotype of urban birds

Urbanization leads to homogenization of avian communities through local extinction of rare bird species and increasing numbers of the same common urban bird species over large geographical areas. Successful city birds often persist through some sort of behavioural plasticity that helps them survive and reproduce close to humans, in built-up areas, with all the typical urban feasts and hazards. In this review, I address whether behavioural plasticity of the acoustic phenotype can be an additional factor in explaining which species end up as urban survivors. Anthropogenic noise has been shown to negatively affect avian distribution and reproduction, especially for species that rely on relatively low-frequency songs for mediating territorial conflicts and attracting partners for mating. Spectral differences between songs of city and forest populations of the same species and correlations between individual song frequency use and local noise levels suggest that many successful city species shift song frequency upward under noisy urban conditions. Experimental evidence has confirmed the ability of several species to show rapid spectral adjustments as well as perceptual benefits of singing at higher frequency in noisy habitats. However, empirical evidence of fitness benefits for birds showing the ability and tendency of noise-dependent spectral adjustment is still lacking. Furthermore, depending on the species and the underlying mechanism for spectral change, there may also be fitness costs through a compromise on signal function. These two aspects are only two of many remaining avenues for future studies. The acoustic phenotype of urban birds provides a great model system to study fundamental processes such as causes and consequences of environmentally induced signal changes, ‘cultural assimilation’, and the relationship between phenotypic and genotypic evolution. Furthermore, the current and expected rate of urbanization remains high at a global scale, which will lead to further spread in time and space of artificially elevated noise levels. This should guarantee the continued interest of scientists, politicians and conservationists for many years ahead.

Applications of Spectral Band Adjustment Factors (SBAF) for Cross-Calibration

To monitor land surface processes over a wide range of temporal and spatial scales, it is critical to have coordinated observations of the Earth's surface acquired from multiple spaceborne imaging sensors. However, an integrated global observation framework requires an understanding of how land surface processes are seen differently by various sensors. This is particularly true for sensors acquiring data in spectral bands whose relative spectral responses (RSRs) are not similar and thus may produce different results while observing the same target. The intrinsic offsets between two sensors caused by RSR mismatches can be compensated by using a spectral band adjustment factor (SBAF), which takes into account the spectral profile of the target and the RSR of the two sensors. The motivation of this work comes from the need to compensate the spectral response differences of multispectral sensors in order to provide a more accurate cross-calibration between the sensors. In this paper, radiometric cross-calibration of the Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) sensors was performed using near-simultaneous observations over the Libya 4 pseudoinvariant calibration site in the visible and near-infrared spectral range. The RSR differences of the analogous ETM+ and MODIS spectral bands provide the opportunity to explore, understand, quantify, and compensate for the measurement differences between these two sensors. The cross-calibration was initially performed by comparing the top-of-atmosphere (TOA) reflectances between the two sensors over their lifetimes. The average percent differences in the long-term trends ranged from -5% to +6%. The RSR compensated ETM+ TOA reflectance (ETM+*) measurements were then found to agree with MODIS TOA reflectance to within 5% for all bands when Earth Observing-1 Hyperion hyperspectral data were used to produce the SBAFs. These differences were later reduced to within 1% for all bands (except band 2) by using Environmental Satellite Scanning Imaging Absorption Spectrometer for Atmospheric Cartography hyperspectral data to produce the SBAFs.

Radiometric Cross-Calibration of EO-1 ALI With L7 ETM+ and Terra MODIS Sensors Using Near-Simultaneous Desert Observations

The Earth Observing-1 (EO-1) satellite was launched on November 21, 2000, as part of a one-year technology demonstration mission. The mission was extended because of the value it continued to add to the scientific community. EO-1 has now been operational for more than a decade, providing both multispectral and hyperspectral measurements. As part of the EO-1 mission, the Advanced Land Imager (ALI) sensor demonstrates a potential technological direction for the next generation of Landsat sensors. To evaluate the ALI sensor capabilities as a precursor to the Operational Land Imager (OLI) onboard the Landsat Data Continuity Mission (LDCM, or Landsat 8 after launch), its measured top-of-atmosphere (TOA) reflectances were compared to the well-calibrated Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) sensors in the reflective solar bands (RSB). These three satellites operate in a near-polar, sun-synchronous orbit 705 km above the Earth's surface. EO-1 was designed to fly one minute behind L7 and approximately 30 minutes in front of Terra. In this configuration, all the three sensors can view near-identical ground targets with similar atmospheric, solar, and viewing conditions. However, because of the differences in the relative spectral response (RSR), the measured physical quantities can be significantly different while observing the same target. The cross-calibration of ALI with ETM+ and MODIS was performed using near-simultaneous surface observations based on image statistics from areas observed by these sensors over four desert sites (Libya 4, Mauritania 2, Arabia 1, and Sudan 1). The differences in the measured TOA reflectances due to RSR mismatches were compensated by using a spectral band adjustment factor (SBAF), which takes into account the spectral profile of the target and the RSR of each sensor. For this study, the spectral profile of the target comes from the near-simultaneous EO-1 Hyperion data over these sites. The results indicate that the TOA reflectance measurements for ALI agree with those of ETM+ and MODIS to within 5% after the application of SBAF.