Radiometric Intercomparison between Suomi-NPP VIIRS and Aqua MODIS Reflective Solar Bands Using Simultaneous Nadir Overpass in the Low Latitudes

Abstract

On-orbit radiometric performance of the Suomi National Polar-Orbiting Partnership (Suomi-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) is studied using the extended simultaneous nadir overpass (SNO-x) approach. Unlike the traditional SNO analysis of data in the high latitudes, this study extends the analysis to the low latitudes-in particular, over desert and ocean sites with relatively stable and homogeneous radiometric properties-for intersatellite comparisons. This approach utilizes a pixel-by-pixel match with an efficient geospatial matching algorithm to map VIIRS data into the Moderate Resolution Imaging Spectroradiometer (MODIS). VIIRS moderate-resolution bands M-1 through M-8 are compared with Aqua MODIS equivalent bands to quantify radiometric bias over the North African desert and over the ocean. Biases exist between VIIRS and MODIS in several bands, primarily because of spectral differences as well as possible calibration uncertainties, residual cloud contamination, and bidirectional reflectance distribution function (BRDF). The impact of spectral differences on bias is quantified by using the Moderate Resolution Atmospheric Transmission (MODTRAN) and hyperspectral measurements from the Earth Observing-1 (EO-1) Hyperion and the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS). After accounting for spectral differences and bias uncertainties, the VIIRS radiometric bias over desert agrees with MODIS measurements within 2% except for the VIIRS shortwave infrared (SWIR) band M-8, which indicates a nearly 3% bias. Over ocean, VIIRS agrees with MODIS within 2% by the end of January 2013 with uncertainty less than 1%. Furthermore, VIIRS bias relative to MODIS is also computed at the Antarctica Dome C site for validation and the result agrees well within 1% with the bias estimated using SNO-x over desert.

Marine boundary layer cloud property retrievals from high-resolution ASTER observations: case studies and comparison with Terra MODIS

“…Likewise, the remaining bias between R 2.1,aA and R 2.1,M is about 0.3 %. These values are in the range of the intercomparison results by Uprety et al (2013), who reported radiometric bias uncertainties between the Suomi National Polar-Orbiting Partnership (Suomi NPP) VIIRS and MODIS in the range of 2-3 % for the VNIR and SWIR bands. It is important to note that small differences in cloud top reflectances could result in possibly large differences in retrieved cloud properties.…”

Towards a long-term global aerosol optical depth record: applying a consistent aerosol retrieval algorithm to MODIS and VIIRS-observed reflectance

“…Although not all DT bands have been compared consistently, the general conclusion was that at least some of the VIIRS bands appear to be biased high as compared to MODIS. The Uprety et al (2013) study indicated that the VIIRS M4 (0.55 µm), M5 (0.67 µm), M7 (0.86 µm) and M8 (1.24 µm) bands had residual high biases of 1.6, 1.3, 2.2 and 3.5 %, respectively, (with error bars of 1-2 %). Based on personal communication, S. Uprety (2014) suggested that the M11 band (2.26 µm) also appears to have a high bias, but more study was required.…”

“…For example, aerosols have decreased dramatically over eastern Europe and increased over India and China (Chin et al, 2013). Regional aerosol changes (Zhang and Reid, 2010) affect regional weather and local air quality, with regional effects having global consequences, including health (e.g., van Donkelaar et al, 2010) and economic consequences (Lin et al, 2014). Therefore, it is imperative that the community has a consistent, long-term aerosol data set, which is global in construct, but with resolution and accuracy sufficient to resolving regional trends.…”

“…VIIRS on S-NPP orbits at 824 km, compared to MODIS aboard Aqua orbiting from 705 km, and has a larger sensor view zenith angle (±70 • compared to ±64 • for MODIS), which both allow VIIRS to have a significantly larger ground swath than MODIS (3040 km compared to 2330 km for MODIS). Although VIIRS and MODIS-Aqua both have similar local equator crossing times (1.30 p.m.), they overlap exactly (viewing a target from nadir and at the same time) only every 3 days and only over polar sites (Uprety et al, 2013). Over a given mid-latitude or tropical site, MODIS and VIIRS observe with varying offsets, ranging from a few minutes apart (with similar solar/viewing geometry) on some days, to multiple hours apart (with different geometry) on others.…”

“…In this direction, Uprety et al (2013) and others have compared MODIS-Aqua and VIIRS over near-SNOs located in the tropics and mid-latitudes. Although not all DT bands have been compared consistently, the general conclusion was that at least some of the VIIRS bands appear to be biased high as compared to MODIS.…”