Terra and Aqua MODIS TEB Inter-Comparison Using Himawari-8/AHI as Reference

Intercomparison between the two MODIS instruments is very useful for both the instrument calibration and its uncertainty assessment. Terra and Aqua MODIS have almost identical relative spectral response, spatial resolution, and dynamic range for each band, so the site-dependent effect from spectral mismatch for their comparison is negligible. Major challenges in cross-sensor comparison of instruments on different satellites include differences in observation time and view angle over selected pseudoinvariant sites. The simultaneous nadir overpasses (SNO) between the two satellites are mostly applied for comparison and the scene under SNO varies. However, there is a dearth of SNO between the Terra and Aqua. This work focuses on an intercomparison method for MODIS thermal emissive bands using Himawari-8 Advanced Himawari Imager (AHI) as a reference. Eleven thermal emissive bands on MODIS are at least to some degree spectrally matched to the AHI bands. The sites selected for the comparison are an ocean area around the Himawari-8 suborbital point and the Strzelecki Desert located south of the Himawari-8 suborbital point. The time difference between the measurements from AHI and MODIS is <5 min. The comparison is performed using 2017 collection 6.1 L1B data for MODIS. The MODISAHI difference is corrected to remove the view angle dependence. The TerraAqua MODIS difference for the selected TEB is up to 0.6 K with the exception of band 30. Band 30 has the largest difference, which is site dependent, most likely due to a crosstalk effect. Over the ocean, the band 30 difference between the two MODIS instruments is around 1.75 K, while over the desert; the difference is around 0.68 K. The MODIS precision is also compared from the Gaussian regression of the double difference. Terra bands 27 to 30 have significant extra noise due to crosstalk effects on these bands. These TerraAqua comparison results are used for MODIS calibration assessments and are beneficial for future calibration algorithm improvement. The impact of daytime measurements and the scene dependence are also discussed

Using Lunar Observations to Assess Terra MODIS Thermal Emissive Bands Calibration

MODIS collects data in both the reflected solar and thermal emissive regions using 36 spectral bands. The center wavelengths of these bands cover the3.7 to 14.24 micron region. In addition to using its on-board calibrators (OBC), which include a full aperture solar diffuser (SD) and a blackbody (BB), lunar observations have been scheduled on a regular basis to support both Terra and Aqua MODIS on-orbit calibration and characterization. This paper provides an overview of MODIS lunar observations and their applications for the reflective solar bands (RSB) and thermal emissive bands (TEB) with an emphasis on potential calibration improvements of MODIS band 21 at 3.96 microns. This spectral band has detectors set with low gains to enable fire detection. Methodologies are proposed and examined on the use of lunar observations for the band 21 calibration. Also presented in this paper are preliminary results derived from Terra MODIS lunar observations and remaining challenging issues

Video game streaming and their communities of play in UK and China

This paper will explore the culture of social video game consumption in the UK and China and the impact of commercial structures upon the social interaction between streamers and their audiences. Through a comparative analysis of literature reviewing video game streaming and viewing practices in each region and thematic analysis of streamer interviews and viewer surveys, we define the social and commercial conventions of Western and Chinese streaming platform approaches. Through the lenses of communities of play (Dekoven, 2002) and outsidership (Johanson and Vahlne, 2009) we seek to understand their differences, effect on socialisation and the potential implications for streamers, audiences and game developers seeking to engage with Chinese and Western streaming platforms

Video game streaming and their communities of play in UK and China

This paper will explore the culture of social video game consumption in the UK and China and the impact of commercial structures upon the social interaction between streamers and their audiences. Through a comparative analysis of literature reviewing video game streaming and viewing practices in each region and thematic analysis of streamer interviews and viewer surveys, we define the social and commercial conventions of Western and Chinese streaming platform approaches. Through the lenses of communities of play (Dekoven, 2002) and outsidership (Johanson and Vahlne, 2009) we seek to understand their differences, effect on socialisation and the potential implications for streamers, audiences and game developers seeking to engage with Chinese and Western streaming platforms

Band-to-Band Misregistration of the Images of MODIS On-Board Calibrators and Its Impact to Calibration

The MODIS instruments aboard Terra and Aqua satellites are radiometrically calibrated on-orbit with a set of onboard calibrators (OBC) including a solar diffuser (SD), a blackbody (BB) and a space view (SV) port through which the detectors can view the dark space. As a whisk-broom scanning spectroradiometer, thirty-six MODIS spectral bands are assembled in the along-scan direction on four focal plane assemblies (FPA). These bands capture images of the same target sequentially with the motion of a scan mirror. Then the images are co-registered on board by delaying appropriate band dependent amount of time depending on the band locations on the FPA. While this co-registration mechanism is functioning well for the "far field" remote targets such as Earth view (EV) scenes or the Moon, noticeable band-to-band misregistration in the along-scan direction has been observed for near field targets, in particular the OBCs. In this paper, the misregistration phenomenon is presented and analyzed. It is concluded that the root cause of the misregistration is that the rotating element of the instrument, the scan mirror, is displaced from the focus of the telescope primary mirror. The amount of the misregistration is proportional to the band location on the FPA and is inversely proportional to the distance between the target and the scan mirror. The impact of this misregistration to the calibration of MODIS bands is discussed. In particular, the calculation of the detector gain coefficient m1 of bands 8-16 (412 nm 870 nm) is improved by up to 1.5% for Aqua MODIS

Initial Investigation of the Angular Dependence of the NOAA-20 VIIRS Solar Diffuser BRDF Change Factor

The NOAA-20 (formerly the Joint Polar Satellite System-1) satellite was launched on November 18, 2017. One of the five scientific instruments aboard the NOAA-20 satellite (N20) is the Visible Infrared Imaging Radiometer Suite (VIIRS). The VIIRS scans the earth surface in 22 spectral bands, of which 14 are denoted as the reflective solar bands (RSBs) with design band central wavelengths from 412 to 2250 nm. The VIIRS regularly performs on-orbit radiometric calibration of its RSBs, primarily through observations of an onboard sunlit solar diffuser (SD). The on-orbit change of the SD bidirectional reflectance distribution function (BRDF) value, denoted as the H-factor, is determined by an onboard solar diffuser stability monitor (SDSM). We have shown that the H-factor for the SD on the VIIRS instrument on the Suomi National Polar-orbiting Partnership (SNPP) satellite is both incident and outgoing sunlight direction dependent. This angular dependence profoundly affects the on-orbit radiometric calibration process and results. Here, we give preliminary results for the angular dependence for the N20 VIIRS SD H-factor, and compare the dependence with that for the SNPP VIIRS

Initial Determination of the NOAA-20 VIIRS Screen Transmittances with Both Yaw Maneuver and Regular on Orbit Data

One of the scientific instruments aboard the NOAA-20 satellite is the Visible Infrared Imaging Radiometer Suite (VIIRS). The VIIRS regularly performs on-orbit radiometric calibration of its reflective solar bands, primarily through observations of an onboard sunlit solar diffuser (SD). The incident sunlight passes through an attenuation screen (the SD screen) and scatters off the SD to provide a radiance source for the calibration. The on-orbit change of the SD bidirectional reflectance distribution function (BRDF), denoted as the H-factor, is determined by an onboard solar diffuser stability monitor (SDSM). The eight SDSM detectors observe the sun through another attenuation screen (the SDSM screen) and the sunlit SD almost at the same time to measures the SD BRDF change. The products of the SD screen transmittance and the BRDF at t=0 and the SDSM screen transmittance were measured prelaunch. Large undulations in the H-factor were seen when using the prelaunch screen transmittances. Fifteen on-orbit yaw maneuvers were performed to validate and to further characterize the screens. Although significantly improved, the H-factor from the yaw maneuver data determined screen transmittance still has undulations as large as about 0.7-0.8%, revealing that the angular step size of the yaw maneuvers is too large. In this paper, we add regular on-orbit data to the yaw maneuver data to further improve the relative products and the relative SDSM screen transmittance. The H-factor time series derived from the newly determined screen transmittance is much smoother than that derived from using only the yaw maneuver data and thus improves considerably the radiometric calibration accuracy

Subsample Difference Correction for Terra MODIS SWIR Bands 5-7 Using Lunar Observations

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the key instruments on board the Terra (EOS (Earth Observing Satellite) AM-1) spacecraft. MODIS has 36 spectral bands ranging in wavelength between 0.4 and 14.2 microns, at three spatial resolutions of 250 meters (bands 1-2), 500 meters (bands 3-7), and 1 kilometer (bands 8-36). For each 1-km sample, the 250-m and 500-m bands use 4 and 2 detectors with each acquiring 4 and 2 subsamples respectively in order to maintain consistent along-scan and along-track resolutions at nadir. The SWIR (Short-Wave Infrared) bands, 57 and 26, share the same focal-plane array as the 1-km thermal emissive bands, 20-25. During one of the two 500-m subsamples for bands 57, sampling of the 1-km bands introduces increased electronic crosstalk contamination, resulting in a subsample difference for both Earth-view and on-board calibrator observations. For this work, we use data from lunar and on-board blackbody observations, which occur at different signal levels for bands 20-25, to derive a correction to the contamination. This correction can be applied to reduce the subsample differences in the MODIS Earth-view data over a wide range of scenes. The impact of this correction on the sensor calibration and Earth-view data will be assessed

Results of MODIS Band-to-Band Registration Characterization Using On-Orbit Lunar Observations

Since launch, lunar observations have been made regularly by both Terra and Aqua MODIS and used for a number of sensor calibration and characterization related applications, including radiometric stability monitoring, spatial characterization, optical leak and electronic cross-talk characterization, and calibration inter-comparison. MODIS has 36 spectral bands with a total of 490 individual detectors. They are located on four focal plane assemblies (FPA). This paper focuses on the use of MODIS lunar observations to characterize its band-to-band registration (BBR). In addition to BBR, the approach developed by the MODIS Characterization Support Team (MCST) can be used to characterize MODIS detector-to-detector registration (DDR). Long-term BBR results developed from this approach are presented and compared with that derived from a unique on-board calibrator (OBC). Results show that on-orbit changes of BBR have been very small for both Terra and Aqua MODIS and this approach can be applied to other remote sensing instruments