Accurate Radiometric Calibration Research Articles

Radiometric calibration evaluation for RSBs of Suomi-NPP/VIIRS and Aqua/MODIS based on the 2015 Dunhuang Chinese Radiometric Calibration Site in situ measurements

ABSTRACTThe Dunhuang Chinese Radiometric Calibration Site (CRCS), used for the vicarious calibration (VC) of reflective solar bands (RSBs), was determined as the primary radiometric calibration site for Chinese space-borne optical sensors and was also selected in 2008 by the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites as one of the instrumented reference sites. In August 2015, an in situ measurement was carried out at the Dunhuang site to evaluate the RSB radiometric calibration of the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi National Polar-orbiting Partnership (NPP) and Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua based on the reflectance-based method. A portable spectroradiometer was used in the experiment to obtain the surface reflectance, and the atmospheric parameters were obtained by sun photometers and radiosonde. A Dunhuang surface bidirectional reflectance distribution function model obtained during the field missions in 2008 and 2013 was implemented. Two days of in situ measurement data including 2 days of VIIRS data and 1 day of MODIS data were used for this evaluation. The results show that the radiometric calibration accuracy is within ±2% for most NPP/VIIRS and Aqua/MODIS RSBs based on the Dunhuang site. It should be noted that there is a relatively large difference in the NPP/VIIRS day–night band (DNB) and Aqua/MODIS band 7 results at the central wavelength of 2.1 μm, with biases of – 4.78% and – 5.71%, respectively. One factor contributing to the difference is the atmospheric transmittance calculation in these bands using the 6S radiative transfer model. If Moderate Resolution Atmospheric Transmission model is used for atmospheric transmittance correction, part of the bias of the MODIS band 7 and VIIRS DNB can be eliminated. However, the consistency of the VIIRS M11 and MODIS B7 is 3.47%, which is larger than that of the other bands.

Atmospheric correction of hyperspectral airborne GCAS measurements over the Louisiana Shelf using a cloud shadow approach

ABSTRACTAs an image-driven method to correct for atmospheric effects, the cloud shadow (CS) approach does not require accurate radiometric calibration of the sensor, making it feasible to process remotely sensed data when radiometric calibration may contain non-negligible uncertainties. Using measurements from the Geostationary Coastal and Air Pollution Events Airborne Simulator and from the Moderate Resolution Imaging Spectroradiometer over the Louisiana Shelf, we evaluate the CS approach to airplane measurements in turbid-water environments. The original CS approach somehow produced remote-sensing reflectance (Rrs, sr−1) with an abnormal spectral shape, likely a result of the assumption of identical path radiance for the pair of pixels in and out of the shadow, which is not exactly valid for measurements made from a low-altitude airplane. To overcome this limitation, an empirical scheme using an effective wavelength-dependent radiance reflectance for the cloud (γ, sr−1) was developed and reasonable GCAS Rrs retrievals are then generated, which were further validated against in situ Rrs. Issues and challenges in applying CS to measurements of low-altitude airplanes are discussed.

A new multichannel threshold algorithm based on radiative transfer characteristics for detecting fog/low stratus using night-time NPP/VIIRS data

ABSTRACTThe Visible Infrared Imager Radiometer Suite (VIIRS) with 22 imagery and radiometric spectral bands on board the Suomi National Polar-orbiting Partnership (NPP) provides imagery products with accurate radiometric calibration and high resolution in space and time. In this article, a multichannel threshold algorithm based on radiative transfer characteristics (MRTC) using VIIRS products is proposed to monitor fog and low stratus at night. Sensitivity analysis of the top-of-atmosphere (TOA) reflectance of fog/low stratus on various influential factors is performed; thus, a reflectance threshold lookup table from various observation geometries is established. Pixels with suitable reflectance are detected as fog/low stratus preliminarily. The final results are confirmed by removing snow pixels and high/medium cloud pixels, and testing the surface homogeneity. Validation experiments are then performed on five typical cases of heavy fog/low stratus with more than a half moon in China using three detection algorithms. This indicates that in some examples the MRTC algorithm achieves some improvements over the existing two algorithms with about a 0.1323 average false alarm ratio (FAR), a 0.8587 average probability of detection (POD), and a 0.7595 average critical success index (CSI).

High-Resolution NDVI from Planet’s Constellation of Earth Observing Nano-Satellites: A New Data Source for Precision Agriculture

Planet Labs (“Planet”) operate the largest fleet of active nano-satellites in orbit, offering an unprecedented monitoring capacity of daily and global RGB image capture at 3–5 m resolution. However, limitations in spectral resolution and lack of accurate radiometric sensor calibration impact the utility of this rich information source. In this study, Planet’s RGB imagery was translated into a Normalized Difference Vegetation Index (NDVI): a common metric for vegetation growth and condition. Our framework employs a data mining approach to build a set of rule-based regression models that relate RGB data to atmospherically corrected Landsat-8 NDVI. The approach was evaluated over a desert agricultural landscape in Saudi Arabia where the use of near-coincident (within five days) Planet and Landsat-8 acquisitions in the training of the regression models resulted in NDVI predictabilities with an r2 of approximately 0.97 and a Mean Absolute Deviation (MAD) on the order of 0.014 (~9%). The MAD increased to 0.021 (~14%) when the Landsat NDVI training image was further away (i.e., 11–16 days) from the corrected Planet image. In these cases, the use of MODIS observations to inform on the change in NDVI occurring between overpasses was shown to significantly improve prediction accuracies. MAD levels ranged from 0.002 to 0.011 (3.9% to 9.1%) for the best performing 80% of the data. The technique is generic and extendable to any region of interest, increasing the utility of Planet’s dense time-series of RGB imagery.

Radiometric Inter-Calibration between Himawari-8 AHI and S-NPP VIIRS for the Solar Reflective Bands

The Advanced Himawari Imager (AHI) on-board Himawari-8, which was launched on 7 October 2014, is the first geostationary instrument housed with a solar diffuser to provide accurate onboard calibrated data for the visible and near-infrared (VNIR) bands. In this study, the Ray-matching and collocated Deep Convective Cloud (DCC) methods, both of which are based on incidently collocated homogeneous pairs between AHI and Suomi NPP (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS), are used to evaluate the calibration difference between these two instruments. While the Ray-matching method is used to examine the reflectance difference over the all-sky collocations with similar viewing and illumination geometries, the near lambertian collocated DCC pxiels are used to examine the difference for the median or high reflectance scenes. Strong linear relationships between AHI and VIIRS can be found at all the paired AHI and VIIRS bands. Results of both methods indicate that AHI radiometric calibration accuracy agrees well with VIIRS data within 5% for B1-4 and B6 at mid and high reflectance scenes, while AHI B5 is generally brighter than VIIRS by ~6%–8%. No apparent East-West viewing angle dependent calibration difference can be found at all the VNIR bands. Compared to the Ray-matching method, the collocated DCC method provides less uncertainty of inter-calibration results at near-infrared (NIR) bands. As AHI has similar optics and calibration designs to the GOES-R Advanced Baseline Imager (ABI), which is currently scheduled to launch in fall 2016, the on-orbit AHI data provides a unique opportunity to develop, test and examine the cal/val tools developed for ABI.

Three Cases of a New Multichannel Threshold Technique to Detect Fog/Low Stratus during Nighttime Using SNPP Data

Abstract The day–night band (DNB) low-light-level visible sensor, mounted on the Suomi–National Polar-Orbiting Partnership (SNPP) satellite, can measure visible radiances from the earth and atmosphere (solar/lunar reflection, and natural/anthropogenic nighttime light emissions) during both day and night and can achieve unprecedented nighttime low-light-level imaging with its accurate radiometric calibration and fine spatiotemporal resolution. Based on the good characteristics of DNB, a multichannel threshold (MCT) algorithm combining DNB with other Visible–Infrared Imager–Radiometer Suite (VIIRS) channels is proposed to monitor nighttime fog/low stratus. Through a gradual separation of the underlying surface (land, vegetation, water bodies, and city lights), snow, and high/medium clouds, a fog/low-stratus region can ultimately be extracted by the algorithm. Then, the algorithmic feasibility is verified by three typical cases of heavy fog/low stratus in China. The experimental results demonstrate that the outcomes of the MCT algorithm approximately coincide with the ground-measured results. Furthermore, the MCT algorithm shows promise for nighttime fog/low-stratus detection in some example cases with about a 0.84 average probability of detection (POD), a 0.73 average critical success index (CSI), and a 0.15 average false alarm ratio (FAR), which reveals some improvement over the conventional dual-channel difference (DCD) algorithm.

An integrated method to improve the GOES Imager visible radiometric calibration accuracy

A variety of vicarious calibration methods over different reference targets have been studied at National Oceanic and Atmospheric Admission (NOAA)/National Environmental Satellite, Data, and Information Service (NESDIS) to provide sensor degradation information for the GOES Imager visible channels which do not have any on-board calibration devices. To meet the increasing demand for more accurate satellite measurements, an integrated method is developed mainly to improve the relative calibration accuracy by combining the results from different vicarious methods. In this study, three commonly used vicarious calibration methods, the desert, Deep Convective Cloud (DCC) and ray-matching methods, are applied to the GOES-12 Imager visible data to describe the integrated method. The integrated method first combines the normalized observations of each individual method by anchoring the results on the first day of satellite operation, and then removes the deviated combined observations using a recursive filtering method. This integration is based on the fact that the GOES sensor trending functions from different methods are very similar within 1% difference over the 7-year study period. The trending uncertainty of the integrated method is less than that of each individual one. The absolute calibration of the integrated method can be achieved by generating the calibration coefficients using the reflectance of reference targets which are well characterized with the Aqua MODIS Collection 6 (C6) data. It is found that there is less than 1% difference between the calibration coefficients derived with the DCC and desert reference targets. It is expected that this integrated method will be a useful tool to validate the GOES-R ABI on-board radiometric calibration accuracy for the solar reflective channels.

Absolute calibration of an analog InSb detector based on multimode spatial correlation of correlated photons

Absolute calibration can be realized by means of correlation photon which is generated by the parametric down conversion. The main difficulty lies in obtaining correlation information about photon flux when this method is applied to analog detector calibration process. A novel method of processing the photocurrent on the basis of detecting multimode spatial correlation is proposed. By converting the charge quantity contained in the photocurrent detected in a certain time interval into the photon counting, and by using double channels balance detection and measuring mean photon counts of each model to correct the dual channels fluctuations, the high accuracy calibration of quantum efficiency can be achieved. The photon fluxes of two channels are balanced by inserting an adjustable attenuator in one optical path. The cross section of pumping beam is comparable to the detection area to ensure three-wave colinearity, and the coherent area of the correlation photons is obtained by measuring pump beam waist and lens focus length. With the known detection area, coherence time and coherence area, the average photon number of each mode is computed. This process should be performed under the average photon number of each mode as a reference which could be used for the proportional scaling of equivalent photons of two channels. Based on this new approach, the absolute power responsivity of an InSb detector is calibrated at 3390 nm with correlated photon pairs at 631 and 3390 nm. The calibration procedure and experiments are described and the uncertainty of this method is analyzed. The results show a relative combination uncertainty of about 7.785% for this calibration method, which agrees well with the result independently obtained in the national photoelectronic metrology laboratory within a relative difference of about 3.6%. This result verifies that the quantum efficiency of an analog detector can be calibrated by the correlated photon method, which has potential applications in highly accurate radiometric calibration without external standards.

Radiometric Calibration Methodology of the Landsat 8 Thermal Infrared Sensor

The science-focused mission of the Landsat 8 Thermal Infrared Sensor (TIRS) requires that it have an accurate radiometric calibration. A calibration methodology was developed to convert the raw output from the instrument into an accurate at-aperture radiance. The methodology is based on measurements obtained during component-level and instrument-level characterization testing. The radiometric accuracy from the pre-flight measurements was estimated to be approximately 0.7%. The calibration parameters determined pre-flight were updated during the post-launch checkout period by utilizing the on-board calibration sources and Earth scene data. These relative corrections were made to adjust for differences between the pre-flight and the on-orbit performance of the instrument, thereby correcting large striping artifacts observed in Earth imagery. Despite this calibration correction, banding artifacts (low frequency variation in the across-track direction) have been observed in certain uniform Earth scenes, but not in other uniform scenes. In addition, the absolute calibration performance determined from vicarious measurements have revealed a time-varying error to the absolute radiance reported by TIRS. These issues were determined to not be caused by the calibration process developed for the instrument. Instead, an investigation has revealed that stray light is affecting the recorded signal from the Earth. The varying optical stray light effect is an ongoing subject of evaluation and investigation, and a correction strategy is being devised that will be added to the calibration process.

A Unified Multi-Purpose Calibration Site for Aerial and High Resolution Satellite Sensors

Experience with both analog and digital systems show that laboratory calibration is not necessarily valid in airborne conditions; whereas the advantages of field calibration are that the entire imaging system is calibrated and not alone the optical part; and the parameters determined are valid in operational airborne conditions (Cramer 2004, 2006; Honkavaara et al. International Archives of Photogrammetry”, Remote Sensing and Spatial Information Sciences 36, 2008a, b). The result of calibration and testing is dependent on a number of permanent system factors and systematic and random components associated with camera, imaging system, flight, atmosphere, object and data post-processing (Honkavaara et al. International Archives of Photogrammetry”, Remote Sensing and Spatial Information Sciences 36, 2008a, b) those affect the quality of the raw images produced by the sensors. It is therefore important to calibrate the aerial or satellite imaging sensors in specially designed fields so that the performance of the entire chain is assessed taking into consideration all the influencing factors. In addition to imaging sensors, ISO 19159 for ‘Calibration and validation of remote sensing imagery sensors and data’ also incorporates airborne laser scanners, imaging radar and water borne sonar systems (Kresse 2010). The task of developing uniform practices and standards for field calibration and testing has been taken up by several international working groups but hardly any permanent multipurpose test field like the one in Sjokulla, Finland with facilities for radiometric and spatial resolution calibration and networks of targeted benchmarks for geometric calibration at large, medium and small imaging scales is available. National Remote Sensing Centre’s (NRSC) interest is in sensor’s performance to solve the question of whether the technology will be able to fulfill present standards of map compilation for disaster management support, urban planning & development, cadastral resurvey, utility mapping, corridor mapping for canal, road, rail alignment, etc. those need very accurate data for its effective usage. With this objective a multi-sensor calibration field, first of its kind in India, designed with targets for geometric calibration, radiometric calibration, spatial resolution and height accuracy calibration is under construction in Shadnagar about 50 km away from Hyderabad that would serve aerial sensors and very high resolution satellite sensors better than 1 m.

Vicarious Cross-Calibration of the China Environment Satellite Using Nearly Simultaneously Observations of Landsat-7 ETM+ Sensor

To understand the absolute radiometric calibration accuracy of the HJ-A CCD-1 sensors, image from these sensors were compared to nearly simultaneously image from Landsat-7 ETM+ sensors. Although the HJ-A CCD-1 sensor has almost the same wavelength of each central band and band width as Landsat-7 ETM+ sensor, there is slightly difference in spectral response function (SRF). The impacts of SRF difference effects would produce ~2 % uncertainty in predicting reflectance of HJ-A CCD-1 sensor using Landsat-7 ETM+ sensor. The reflectance observed by satellite at top-of-atmosphere generally depends on its’ geometric conditions. The results reveal that the impacts of geometrical conditions would impact on the vicarious cross-calibration accuracy, which should be removed. The performances of cross-calibration are calibrated and validated by four image pairs collected from Yellow River Delta, China, and Qingdao City, China, at four independent times. The results indicate that the HJ-A CCD-1 sensors can be cross calibrated to the Landsat-7 ETM+ sensors to within an accuracy of 3.99 % (denoted by Relative Root Mean Square Error) of each other in all bands except band 4, which has a 6.33 % difference.

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.

In-situ spectral reflectance measurement of off-axis paraboloidal reflector with a large aperture for radiometric calibration

Off-axis paraboloidal reflector with a large aperture is often used as a collimator in radiometric calibration system in the space environment or a simulator for space carrier. Spectral reflectance measurement of the reflector is an important issue that determines the accuracy of radiometric calibration, especially, for imaging spectrometer. Currently, the reflectance of the reflector is generally measured by the sample contrast method. So, only a small sample of the reflector rather than the whole can be measured. In order to overcome this limitation, a method for in-situ measuring spectral reflectance of off-axis paraboloidal reflector, especially, with a large aperture, is proposed in this paper. First of all, the proposed in-situ measurement approach is designed according to in-situ contrast measurement. Then, the proposed measurement is realized and evaluated in experiment for measuring spectral reflectance of an off-axis paraboloidal reflector with an aperture of 110mm. Finally, the influence of prodigious temperature fluctuation on the measurement is experimentally investigated and the impact of optical devices and environment on the uncertainty is analyzed. The total experimental uncertainty is obtained as 4.2%. The experimental results proved that the spectral reflectance of the reflector will decrease when the experimental temperature falls from 20°C to −100°C and the decrease degree is different for different wavelength bands.

STK를 이용한 고해상도 위성 SAR 운용 및 표적물 추출 기법

A comprehensive SAR(Synthetic Aperture Radar) simulation is considered to be a complicated task since a full knowledge of the signal propagation characteristics, antenna pattern, system internal errors and interference noises should be taken into account. In high resolution target application modes, the time varying nature of target RCS(Radar Cross Section) strongly affects the generated SAR images. In this paper, in-depth SAR simulations are performed and analyzed incorporating the STK tools and MATLAB software. STK provides realistic orbit parameters while its radar module helps to extract accurate radiometric parameters of ground targets. SAR raw data corresponding to a given target is generated and processed using MATLAB simulator. The performance is measured by PSLR(Peak Sidelobe Ratio) and ISLR(Integrated Sidelobe Ratio) for a point target, which can be used as reference parameters for accurate radiometric calibration. Finally, high resolution target simulations are performed by adopting time varying target RCS characteristics.

Rayleigh, Deep Convective Clouds, and Cross-Sensor Desert Vicarious Calibration Validation for the PROBA-V Mission

PROBA-V is a remote sensing satellite mission for global monitoring of vegetation. It is designed to offer almost daily coverage of all land masses and to provide data continuity with the VGT2 instrument aboard SPOT-5. Accurate radiometric calibration is key to the success of the mission; therefore, a comprehensive system for in-flight radiometric calibration has been developed. Without no onboard calibration devices, this in-flight calibration will rely fully on vicarious methods. In total nine techniques for vicarious calibration have been implemented and tested in order to meet the radiometric mission requirements. Three key methods that contribute largely to the calibration performance are presented in this paper: Rayleigh, deep convective clouds, and cross-sensor calibration over stable desert sites. As the PROBA-V sensor has still to be launched, calibration algorithm verification is performed using data from the spectrally very similar SPOT-VGT1 and SPOT-VGT2 sensors.

Radiometric Calibration Accuracy of GOES Sounder Infrared Channels

Quality infrared (IR) radiances and their derived products from the Geostationary Environmental Operational Satellite (GOES) Sounder are very important data sources to weather prediction and nowcasting applications for the continental United States and adjacent ocean regions. With demanding requirements for more accurate weather nowcasting models and climate change studies, it is necessary to assess and improve the radiometric calibration accuracy of the GOES Sounder data. The objective of this paper is to examine the GOES Sounder IR radiometric calibration accuracy, and the diurnal calibration variation using intercalibration with two well-calibrated hyperspectral radiometers onboard low earth orbit satellites, the Atmospheric Infrared Sounder (AIRS) on the Aqua satellite and the Infrared Atmospheric Sounding Interferometer (IASI) on the Metop-A satellite. The results show that most sounder IR channels of GOES-11 through GOES-15 are well calibrated outside of the satellite midnight effect time period, with a less than 0.5 K of mean bias of brightness temperature with respect to IASI. Yet, the impact of the satellite midnight effect on the radiance quality varies greatly at different IR channels among different satellites. Further research is needed to understand the changes of instrument environmental flux on the GOES IR radiance around satellite midnight.

Correction for GOES Imager Spectral Response Function Using GSICS. Part II: Applications

During the Geostationary Operational Environmental Satellite (GOES)-14 and -15 post-launch test (PLT) for science periods, an up to ~ 2 K mean brightness temperature (Tb) bias with respect to collocated Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI) observations was observed in the absorptive IR channels of the GOES-14/15 Imagers. These large scene-dependent biases were believed to be caused mainly by spectral characterization errors. In this paper, we refined the spectral response function (SRF) shift algorithm which was developed during the GOES-13 PLT period to improve the GOES-14/15 Imager IR radiometric calibration accuracy by accurately calculating the impact of blackbody on the calibrated scene radiance. The uncertainty of the SRF shift algorithm was estimated and used to guide the final selection of the total amount of central wave-number shift. This refined algorithm was first verified with GOES-13 Imager Ch6 data and then used to evaluate and further revise the audited GOES-14/15 SRFs provided by the instrument vendor. Based on this algorithm, the optimal SRF shifts were -1.98 cm-1 for GOES-13 Ch6, -8.25 cm-1 for GOES-14 Ch3, -0.25 cm-1 for GOES-14 Ch6, -6.25 cm-1 for GOES-15 Ch3 and +0.50 cm-1 for GOES-15 Ch6. The newly shifted SRFs were operationally implemented into the GOES-14/15 Imager IR calibrations in the August of 2011 and successfully reduced the mean all-sky Tb bias with respect to the reference instrument to less than 0.15 K. The scene-dependent bias, which can be nonlinear at large erroneous SRF, was also greatly reduced. The same method was applied to correct the GOES-12 Imager Ch6 SRF which has a changing SRF error during its mission life. A strong linear relationship between the optimal SRF shifts and the mean Tb bias with respect to the AIRS data was observed at this channel. This strong linear relationship can be used to revise the GOES-12 Ch6 SRF for a better radiance simulation. The method described in this paper is particularly important to evaluate and revise the erroneous SRF, if it exists, after satellite launch yet before it becomes fully operational.

On-orbit radiometric calibration for water-vapor band of FY-2 satellite

With the Moon as a reference source for thermal emissive band(TEB) calibration without any knowledge of lunar surface's emissivity or temperature,the quantitative relationship of the measured radiances between different TEBs is established by introducing the parameter universal dual-band emissivity ratio(UDER).This was further used to deduce a novel cross-calibration approach between different bands.Meanwhile,selecting the thermal infrared band with the highest radiometric accuracy as a baseline,the on-orbit radiometric calibration for water-vapor band of FY-2E satellite is realized by using multi-bands lunar observations without any space-borne full-path blackbody.The radiometric calibration accuracy has been improved by about 3.5 K in the lower temperature region between 200K and 220 K,which is great benefits to the enhancement of some quantitative products significantly,i.e.cloud classification.

Comparison Among Cross, Onboard and Vicarious Calibrations for Terra/ASTER/VNIR

Comparative study on radiometric calibration methods among onboard, cross and vicarious calibration for visible to near infrared radiometers onboard satellites is conducted. The data sources of the aforementioned three calibration methods are different and independent. Therefore, it may say that the reliable Radiometric Calibration Accuracy: RCC would be the RCC which are resemble each other two of three RCCs. As experimental results, it is found that vicarious and cross calibration are reliable than onboard calibration. Also vicarious calibration based cross calibration method is proposed here. The proposed cross calibration method should be superior to the conventional cross calibration method based on band-to-band data comparison. Through experiments, it is also found that the proposed cross calibration is better than the conventional cross calibration. The radiometric calibration accuracy of the conventional cross calibration method can be evaluated by using the proposed cross calibration method.

A Technique For Removing Second-Order Light Effects From Hyperspectral Imaging Data

The Hyperspectral Imager for the Coastal Ocean (HICO) instrument currently on board the International Space Station is a new sensor designed specifically for the studies of turbid coastal waters and large inland lakes and rivers. It covers the wavelength range between 0.4 and 0.9 μm with a spectral resolution of 5.7 nm and a spatial resolution of approximately 90 m. The HICO sensor is not equipped with a second-order blocking filter in front of the focal plane array. As a result, the second-order light from the shorter visible spectral region falls onto the detectors covering the near-IR spectral region above 0.8 μm. In order to have accurate radiometric calibration of the near-IR channels, the second-order light contribution needs to be removed. The water-leaving radiances of these near-IR channels over clear ocean waters are close to zero because of strong liquid water absorption above 0.8 μm. Through analysis of HICO imaging data containing features of shallow underwater objects, such as coral reefs, we have developed an empirical technique to correct for the second-order light effects in near-IR channels. HICO data acquired over Midway Island in the Pacific Ocean and the Bahamas Banks in the Atlantic Ocean are used to demonstrate the effectiveness of the new technique.