RESUMEN
The MODerate-resolution Imaging Spectroradiometer (MODIS) is a premier Earth observing sensor of the early 21st Century, flying on-board the Terra (T) and Aqua (A) spacecrafts. Both instruments far exceeded their 6 year design life and continue to operate satisfactorily for more than 15 and 13 years, respectively. The MODIS instrument is designed to make observations at nearly a 100% duty cycle covering the entire Earth in less than 2 days. The MODIS sensor characteristics include a spectral coverage from 0.41 µm - 14.4 µm, of which those wavelengths ranging from 3.7 µm - 14. 4 µm cover the thermal infrared region which is interspaced in 16 Thermal Emissive Bands (TEB). Each of the TEB contains 10 detectors which record samples at a spatial resolution of 1 km. In order to ensure a high level of accuracy for the TEB measured Top Of Atmosphere (TOA) radiances, an onboard BlackBody (BB) is used as the calibration source. This paper reports the noise characterization and performance of the TEB on various counts. First, the stability of the onboard BB is evaluated to understand the effectiveness of the calibration source. Next, key noise metrics such as the Noise Equivalent Temperature difference (NEdT) and the Noise Equivalent dn difference (NEdN) for the various TEB are determined from multiple temperature sources. These sources include the nominally controlled BB temperature of 290 K for T-MODIS and 285 K for A-MODIS, as well as a BB Warm Up - Cool Down (WUCD) cycle that is performed over a temperature range from roughly 270 K - 315 K. The Space View (SV) port that measures the background signal serves as a viable cold temperature source for measuring noise. In addition, a well characterized Earth View (EV) Target, the Dome C site located in the Antarctic plateau, is used for characterizing the stability of the sensor, indirectly providing a measure of the NEdN. Based on this rigorous characterization, a list of the noisy and inoperable detectors for the TEB for both instruments is reported to provide the science user communities quality control of the MODIS Level 1B calibrated product.
RESUMEN
Contemporary scientists have vested interest in trying to understand the climatology of the North Atlantic Basin since this region is considered as the genesis for hurricane formation that eventually get shipped to the tropical Atlantic region and the Caribbean. The effects of atmospheric water cycle and the climate of West Africa and the Atlantic basin are hugely impacted by the radiative forcing of Saharan dust. The focus area in this paper would be to improve the dust detection schemes by employing the use of multi sensor measurements in the thermal emissive wavelengths using legacy sensors such as Terra (T) and Aqua (A) MODerate-resolution Imaging Spectroradiometer (MODIS), fusing with Ozone Monitoring Instrument (OMI). Previous work by Hao and Qu (2007) had considered a limited number of thermal infrared channels which led to a correlation coefficient R2 value of 0.765 between the Aerosol Optical Thickness (AOT) at 550 nm and the modeled dust index. In this work, we extend the thermal infrared based dust detection by employing additional channels: the 8.55 µm which has shown high sensitivity to the Saharan dust, along with water vapor channel of 7.1 µm and cloud top channel of 13.1 µm. Also, the dust pixels were clearly identified using the OMI based aerosol types. The dust pixels were cleanly segregated from the other aerosol types such as sulfates, biomass, and other carbonaceous aerosols. These improvements led to a much higher correlation coefficient R2 value of 0.85 between the modified dust index and the AOT in comparison to the previous work. The key limitations from the current AOT products based on MODIS and were put to test by validating the improved dust detection algorithm. Two improvements were noted. First, the dust measurement radiometry using MODIS is significantly improved by at least an order of 2. Second the spatial measurements are enhanced by a factor of at least 10.