There are now five hyperspectral infrared sounders in orbit (AIRS, two CrIS instruments, two IASI instruments). A long-term record spanning these instruments and continuing forward with future instruments holds great promise for the study of weather and climate. This long-term record must separate the effects of instrument artifacts and weather variability. We introduce the “StratRad” stratified radiance means product, containing means of groups of spectra for AIRS on Aqua and CrIS on SNPP. We show how this product can be used both to illuminate instrument artifacts and to study common observations of weather patterns at an accuracy of better than 0.1 K. Radiances are stratified by latitude, longitude, day/night, land/sea, and observation angle.
A KHz Pulsed Laser Detection System was developed employing the concept of charge integration with an electrometer, in the NASA Goddard Space Flight Center, Code 618 Calibration Lab for the purpose of using the pulsed lasers for radiometric calibration. Comparing with traditional trans-impedance (current-voltage conversion) detection systems, the prototype of this system consists of a UV-Enhanced Si detector head, a computer controlled shutter system and a synchronized electrometer. The preliminary characterization work employs light sources running in either CW or pulsed mode. We believe this system is able to overcome the saturation issue when a traditional trans-impedance detection system is used with the pulsed laser light source, especially with high peak-power pulsed lasers operating at kilohertz repetition rates (e.g. Ekspla laser or KHz OPO). The charge integration mechanism is also expected to improve the stability of measurements for a pulsed laser light source overcoming the issue of peak-to-peak stability. We will present the system characterizations including signal-to-noise ratio and uncertainty analysis and compare results against traditional trans-impedance detection systems.
The reflective solar bands (RSB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite are primarily calibrated on-orbit by a solar diffuser (SD) panel whose performance is monitored by an accompanying solar diffuser stability monitor (SDSM). In this paper, the SD and SDSM calibration methodology is reviewed and the results from the analysis of the up-to-date three and half years of mission data are presented. With the newly derived product of the SD bidirectional reflectance factors, the vignetting functions for the screens in the SD/SDSM system and the carefully selected “sweet spots”, and the fully illumination region, the artificial seasonal patterns and noises in the derived SD degradation and the RSB calibration coefficients are removed or significantly reduced. The result shows that the SD degrades faster at short wavelengths while the RSB degrades in a much complex pattern.
The region of interest (ROI) extraction is of crucial importance in the preprocessing of object detection, especially when the spatial resolution of the remote sensing image becomes extremely high and the field of view becomes relatively large. To conduct the detection approaches directly on the image usually yields unsatisfactory result, and is time consuming. Saliency models based on visual attention mechanism are the general solution to this problem. However, the conventional saliency models deal with the pixel intensity, color statistics or contrast, while neglect the characteristics and spatial distribution of the ROI, which would results in the false alarm in the extraction. In this paper, taken residential area as the region of interest, a ROI extraction method based on saliency, and enhanced by corner density is proposed. The saliency model is adopted to extract the potential area preliminarily. In spite of the efficiency of the model, it suffers from certain defect, that is, the preliminary extracted region contains plenty of false alarms due to the high contrast of bare land and water reflection. Therefore, corner density feature is constructed to refine the extraction, based on the idea of residential area showing higher edge and corner density compared to rural area. In the experimental part, the proposed method is compared with three saliency models. The experimental results reveal that the proposed method is effective in eliminating the false alarm caused by high intensity or contrast of the pixel.
Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effect that these changes will have on the calibration. First, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. Second, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. We find that RSR changes have a small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% in all cases at any time in the missions, with bands 1, 8, and 9 impacted the most.
The Advanced Baseline Imager (ABI) is a critical instrument onboard GOES-16 which provides high quality Reflective Solar Bands (RSB) data though radiometric calibration using onboard solar diffuser. Intensive field campaign for post-launch validation of the ABI L1B spectral radiance observations was carried out during March-May, 2017 to ensure the SI traceability of ABI. In this paper, radiometric calibrations of the five RSBs of ABI are evaluated with the measurements by Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) onboard the high-altitude aircraft ER2. The ABI MESO data processed by the vendor with ray-matching to AVIRIS-NG during the field campaign was compared with the AVIRIS-NG measurements for radiometric bias evaluation. Furthermore, there were several implementations and updates in the solar calibration of ABI RSBs which resulted in different versions of detector gains and nonlinear calibration factors. These calibrations included the calibration by the operational ground processing system, by vendor and the calibration with updated nonlinear calibration factor table for striping mitigation and accounting for the integration time difference between solar calibration and Earth view. The North-South Scan (NSS) field campaign data of ABI were re-processed with these calibration coefficients to quantitatively evaluate the detector uniformity change. The detector uniformity difference are traced back to the difference in the implementation of the solar calibration.
The first NOAA/NASA Join Polar Satellite System (JPSS-1) satellite was successfully launched on November 18, 2017, becoming NOAA-20. Instruments on-board NOAA-20 satellite include the Visible Infrared Imaging Radiometer Suite (VIIRS). This instrument is the second build of VIIRS, with the first flight instrument on-board NASA/NOAA Suomi National Polar-orbiting Partnership (SNPP) satellite operating since October 2011. The purpose of these VIIRS instruments is to continue the long-term measurements of biogeophysical variables for multiple applications including weather forecasting, rapid response and climate research. The geometric performance of VIIRS is essential to retrieving accurate biogeophysical variables. This paper describes the early on-orbit geometric performance of the JPSS-1/NOAA-20 VIIRS. It first discusses the on-orbit orbit and attitude performance, a key input needed for accurate geolocation. It then discusses the on-orbit geometric characterization and calibration of VIIRS geometry and an initial assessment of the geometric accuracy. This section includes a discussion of an improvement in the geometric model that corrects small geometrical artifacts that appear in the along-scan direction. Finally, this paper discusses on-orbit measurements of the focal length and the impact of this on the scan-to-scan underlap/overlap.
The Spectrometer Arduino Mega (SpAM) is a prism spectrometer that has been designed and fabricated by the Remote Sensing Group (RSG) at the College of Optical Sciences of the University of Arizona. SpAM is designed to be a low budget, stand alone, solar powered field spectrometer. RSG plans to use SpAM to measure the reflectance of natural surfaces in the field. After the laboratory calibration of SpAM, it will be deployed to the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley, Nevada. A satellite uplink will allow RSG to upload SpAM measurements on a daily basis. SpAM measures and records the spectral composition of a light source or light reflected from a surface. The prism inside of SpAM refracts the input light onto a linear array of 512 silicon detectors. The detector-prism combination produces a spectral resolution of ~2 nm, and the overall spectral range is 433–760 nm. The spectral radiometric measurements produced by SpAM are stored and processed by an Arduino mega micro controller with network capabilities for field applications. SpAM will be used to analyze the spectral reflectance of Railroad Valley dry lake, and its accuracy and performance will be determined by a comparison with filter-based radiometers that have been produced by RSG. This work presents the design and instrumentation of SpAM, and an assessment of its ability to provide radiometric results for satellite calibration and other radiometric measurement applications.
Optical and electronic cross-talk effects are present in the Terra MODIS sensor. Those effects are reviewed and the physical (engineering) characteristics that give rise to the effects are described when they are known. The potential for performance degradation also is assessed for each effect. The long-term consequence of these effects is to give rise to Terra MODIS to Aqua MODIS performance trend differences and researchers are cautioned to use care in interpretation of these trend differences as potential diurnal environmental effects.
The radiometric performance of the reflective solar bands (RSBs) of NOAA-20 VIIRS, recently launched on 18 November 2017, is evaluated through an intercomparison with Aqua MODIS. The analysis adapts a “nadir-only” refinement of the simultaneous nadir overpass (SNO) to generate comparison time series for assessment of the on-orbit calibration of NOAA-20 VIIRS RSBs using the official sensor data records (SDRs). The comparison result reveals an unstable and varying early radiometric performance upward of 5%. SNPP VIIRS, the precursor VIIRS, is also used to generate a comparison time series against Aqua MODIS. The result shows that NOAA-20 VIIRS RSBs have a 2 to 8% radiometric deficit relative to SNPP VIIRS RSBs.
With the development of space satellites, a large number of high-resolution remote sensing images have been produced, so the analysis and application of high-resolution remote sensing images are very important. Recently deep learning provides a new method to increase the accuracy of land-cover classification. This study aims to propose a classification framework based on convolutional neural network (CNN) to carry out remote sensing scene classification. After remote sensing images are trained by CNN, a model which can extract complex characteristic from the image for classification is created. In this paper, GaoFen-2(GF-2) satellite data is used as data sources and Jilin province of China is selected as the study area. Firstly, the preprocessed images are made into a GF-2 satellite data sets. Secondly, CaffeNet is used to train the data sets through Caffe platform and the classification result is obtained. The CNN overall accuracy is 89.88%, the Kappa coefficient is 0.8026. Compared with the traditional BP neural network classification result, it is obviously find the CNN is more suitable for remote sensing image classification.
The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on-board the Terra and Aqua space- craft are equipped with several on-board calibrators (OBCs) and continue to operate normally since launch. One such calibrator is the solar diffuser (SD), which allows for the calibration of the 20 reflective solar bands (RSBs) with wavelengths ranging from 0.41 to 2.3 μm. In order to accurately characterize the RSBs on-orbit, the changes associated with the SD bi-directional reflectance factor (BRF) are tracked using a solar diffuser stability monitor (SDSM). The SDSM consists of nine detectors located within a spherical integration source (SIS) and covers wavelengths from 0.41 to 0.94 μm. During each calibration event, the SDSM alternately views sunlight through an attenuation screen and the sunlight reflected from the SD in order to accurately characterize the degradation of the SD at those nine wavelengths. This paper provides a brief overview of the SD/SDSM calibration and operation, with more emphasis on the recent performance of the SD degradation and the SDSM detectors. A methodology to compute the signal-to-noise ratio (SNR) for each of the SDSM detectors is formulated and the noise performance is tracked over the mission lifetime. The importance of the detector noise to the RSB calibration uncertainty and to other instruments, such as the VIIRS SDSM, is also discussed.
The Landsat-9 Operational Land Imager 2 (OLI-2) instrument, currently under development for launch in late 2020, is a clone of the Landsat-8 OLI instrument, which was launched in 2013. Ball Aerospace built and rigorously characterized the Landsat-8 OLI and is repeating the process for the Landsat-9 OLI-2. A major difference between the testing for OLI and OLI-2 will be spectral test equipment. The instrument-level spectral test for OLI made use of a double monochromator; the OLI-2 test will use of Goddard Laser for the Absolute Measurement of Radiance (GLAMR). The GLAMR system is a set of lasers, which collectively cover the entire spectral range of the OLI-2 spectral bands. The laser outputs are fed to a 30 '' integrating sphere via fiber optic cables, which OLI-2 can view from its position inside the thermal vacuum chamber. The laser-based spectral characterization offers several major advantages over the monochromator-based methods: (1) higher signal levels as compared to the lamp in the double monochromator providing better signal to noise and capabilities to measure out of band response, (2) full aperture illumination and flood illumination of multiple focal plane modules so that all detectors are tested and crosstalk effects can be observed, as opposed to the approximately 60 detectors illuminated by the slit image of the monochromator (3) an absolute spectral response characterization as opposed to relative spectral response. OLI-2 spectral testing with GLAMR should begin in late 2018. This work describes the spectral-radiometric test plan, test requirements, and GLAMR performance demonstrated prior to OLI-2 characterization.
A primary objective of the GOES-16 post-launch airborne science field campaign was to provide an independent validation of the SI traceability of the Advanced Baseline Imager (ABI) spectral radiance observations for all detectors post-launch. The GOES-16 field campaign conducted sixteen validation missions (March to May 2017), three of which served as the primary ABI validation missions and are the focus of this work. These validation missions were conducted over ideal Earth targets with an integrated set of well characterized hyperspectral reference sensors aboard a high-altitude NASA ER-2 aircraft. These missions required ABI special collections (to scan all detectors over the earth targets), unique aircraft maneuvers, coordinated ground validation teams, and a diplomatic flight clearance with the Mexican Government. This effort presents a detector-level deep-dive analysis of data from the targeted sites using novel geospatial database and image abstraction techniques to select and process matching pixels between ABI and reference instruments. The ABI reflective solar band performance (ABI bands 1-3 & 5-6) was found to have biases within 5 % radiance for all bands, except band 2; and the ABI thermal emissive band performance was found to have biases within 1 K for all bands. Additional inter-comparison results using targeted ABI special collections with the Low Earth Orbit reference sensor S-NPP/VIIRS will also be discussed. The reference data collected from the campaign has demonstrated that the ABI SI traceability has been validated post-launch and established a new performance benchmark for NOAA’s next generation geostationary Earth observing instrument products.
The Thermal Infrared Sensor-2 (TIRS-2) aboard Landsat 9 will continue Landsat’s four decade-long legacy of providing moderate resolution thermal imagery from low earth orbit (at 705 km) for environmental applications. Like the Thermal Infrared Sensor aboard Landsat 8, it is a pushbroom sensor with a cross-track field of view of 15° and provides two spectral channels at 10.8 and 12 μm. To ensure radiometric, spatial, and spectral performance, a comprehensive pre-launch testing program is being conducted at NASA Goddard Space Flight Center at the component, subsystem, and instrument level. This paper will focus on the results from the subsystem level testing where the instrument is almost completely assembled. This phase of testing is specifically designed to assess imaging performance including focus and stray light rejection, but is also used to provide a preliminary assessments of spatial and spectral performance. The calibration ground support equipment provides a flexible blackbody illumination source and optics to conduct these tests. The spectral response test setup has its own illumination source outside the chamber that propagates through the calibration ground support equipment in an optical configuration designed for this purpose. This test configuration with the calibration ground support equipment and TIRS-2 subsystem in the thermal vacuum chamber enables a large range of illumination angles for stray light measurements. The results show that TIRS-2 performance is expected to meet all of its performance requirements with few waivers and deviations.
With comprehensive analysis of the VIIRS DNB on-board calibrator blackbody (OBCBB) data and Earth View (EV) data, it is shown that the DNB OBCBB data can only track the dark current component of the DNB HGS EV dark offset. The DNB observation of deep space during the spacecraft pitch maneuver was also contaminated by star lights. With these acquired knowledge, we propose an improved algorithm for determining the DNB HGS dark offset that is both free from light contamination and capable of tracking drifts continously. The new algorithm is expected to improve the DNB radiometric performance at low radiance level.
This study presents a modeling approach to improve solar diffuser (SD) degradation determination from SD stability monitor (SDSM) measurements. The MODIS instrument uses a SD to calibrate its reflective solar bands (RSBs) on-orbit. Due to the imperfectly designed SDSM sun view screen, the SD reflectance tracked by SDSM has large noise. The SDSM measurements noise is spectrally coherent and can be minimized by normalizing measurements to the least degraded detector 9 (936 nm). In this study, a SD degradation model is used to determine the SD degradation’s wavelength dependency and the detector 9 degradation is estimated by the model solution. The results show the SD degradations measured at 6 SDSM detectors (554 - 936 nm) have stable relationships, where the degradation is inversely proportion to 1/wavelength^4. The model estimated SD degradation at SDSM detector 9 wavelength (936 nm) is ~0.9% from 2002 to 2018. Based on the SD degradation model solution, the SD degradation at short/mid wave bands are estimated to improve short/mid wave bands calibration. The model can also be used to improve interpolating SD degradation at SDSM detectors to RSB wavelengths. Compared to linear interpolation, bands 9 and 10 show the largest differences of up to 0.3 and 0.4% respectively. These differences directly impact the calibration coefficients of these bands.
The AQUA, SNPP, and NOAA 18-20 PM sun-synchronous satellites were designed with similar local time, local solar zenith angles, and overlapping temporal coverage. Although the satellites are expected to have fixed local equator- crossing time, during the satellite lifetime, the equator-crossing times of these satellites drift. For NOAA 18-19, the drift in equator-crossing time is significant (few hours) and no correction has been done over the lifetime. For SNPP and AQUA, correction in the orbital inclination angle was periodically performed to maintain the equator-crossing time around the designed value. The impact of systematic drift of the local observation time during the satellite life cycle can be significant and should be accounted for when using multi-year time series of satellite products in long-term environmental studies. In this paper, the equator-crossing time drift of AQUA, SNPP, and NOAA 18-20, the correction of SNPP and AQUA equator-crossing time via orbital inclination angle change, and the consequent local solar zenith angle variation are evaluated. The impact of such drift on low-latitude mean brightness temperature trend derived from the similar ~11 μm thermal emissive channel of AQUA MODIS CH31, SNPP Visible Infrared Imaging Radiometer Suite (VIIRS) CH15 and NOAA 18-19 HIRS CH08 are analyzed. The drift in the mean brightness temperature measured by these sensors is combined as a function of local time and analyzed using diurnal cycle analysis. The mean brightness temperature drift for SNPP VIIRS is reconciled within the context of much larger temperature drift of NOAA 18-19.
The Atmospheric Infrared Sounder (AIRS) radiometric calibration coefficients convert the counts measured from the instruments A/D converters (Level 1A) to SI traceable radiance units (Level 1B). The calibration equations are based on how the instrument operates and follow a simple second order relationship between counts and radiance. Terms are included to account for nonlinearity of the detectors, emissivity and temperature knowledge of the on-board calibrator (OBC) blackbody and radiometric offset due to coupling of the polarization of the scan mirror with the spectrometer. In this paper, we re-derive the radiometric calibration equation with a little more rigor and account for the view angle of each of the 4 space views. We then derive new polarization coefficients from the 4 space views over the mission and use them re-derive the coefficients for blackbody emissivity and nonlinearity. We then compare new coefficients (Version 7k) with the latest operational version of the AIRS radiometric calibration coefficients (Version 5). The AIRS Version 5 coefficients were sufficiently adequate that an update has never been made since AIRS launch in 2002. However, it can be seen, when we compare to the Cross-track Infrared Sounder (CrIS), that better agreement is made in Version 7. The impact of the new coefficients is highest at cold scene temperatures and very warm temperatures.
In 2015, NSPO (National Space Organization) began to develop the sub-meter resolution optical remote sensing instrument of the next generation optical remote sensing satellite which follow-on to FORMOSAT-5. The multi-spectral strip filter has been developed by NSPO in collaboration with MORRISON Opto-Electronics (MOE) Ltd, meeting the emerging demands of the new TDI CMOS image sensor of the Korsch type optical remote sensing instrument for next satellite mission. This paper represents the technology to deposit the multi-spectral band-pass strip filters on single synthetic silica substrate. The optical multi strip filter is installed in front of TDI CMOS image sensor to capture multi-spectral images of the earth surface. The optical multi strip filter composed of five band-pass filters on single substrate, including three bands in visible bands (400nm to 700nm) called VIS, one panchromatic band including whole visible spectrum and one band in near infrared (NIR). MORRISON Opto-Electronics (MOE) Ltd is responsible to integrate micro-structuring process base on lithography and ion beam-assisted deposition (IAD). These made multi spectral optical thin film coating in a small area with high dimension accuracy deposited possible on the substrate and achieve the robust process of patterning photoresist and removing the photoresist. By repeating the process five times, we have deposited five kinds of band-pass strip filters on single substrate.
