Impact of MODIS sensor calibration updates on Greenland Ice Sheet surface reflectance and albedo trends

Abstract

Abstract. We evaluate Greenland Ice Sheet (GrIS) surface reflectance and albedo trends using the newly released Collection 6 (C6) MODIS (Moderate Resolution Imaging Spectroradiometer) products over the period [2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016]. We find that the correction of MODIS sensor degradation provided in the new C6 data products reduces the magnitude of the surface reflectance and albedo decline trends obtained from previous MODIS data (i.e., Collection 5, C5). Collection 5 and 6 data product analysis over GrIS is characterized by surface (i.e., wet vs. dry) and elevation (i.e., 500-2000 m, 2000 m and greater) conditions over the summer season from 1 June to 31 August. Notably, the visible-wavelength declining reflectance trends identified in several bands of MODIS C5 data from previous studies are only slightly detected at reduced magnitude in the C6 versions over the dry snow area. Declining albedo in the wet snow and ice area remains over the MODIS record in the C6 product, albeit at a lower magnitude than obtained using C5 data. Further analyses of C6 spectral reflectance trends show both reflectance increases and decreases in select bands and regions, suggesting that several competing processes are contributing to Greenland Ice Sheet albedo change. Investigators using MODIS data for other ocean, atmosphere and/or land analyses are urged to consider similar re-examinations of trends previously established using C5 data.

Characterization of Canadian High Arctic glacier surface albedo from MODIS C6 data, 2001–2016

“…This approach is consistent with previous work using MCD43A3 data (e.g. Alexander et al, 2014;Tedesco et al, 2016;Casey et al, 2017). 140…”

“…Comparison of the MODIS C5 and C6 full inversion albedo data from the Greenland Ice Sheet confirmed many of the broad spatial patterns in surface albedo identified in the C5 data, but the magnitude of the C6 albedo change was much smaller (Casey et al, 2017).…”

“…This vicarious calibration approach has improved the precision of C6 reflectances, and it also mitigates long-term 110 sensor drift, particularly at the shorter wavelengths. The C6 post-calibration residual error is on the order of several tenths of one percent for top of the atmosphere (TOA) reflectance (Lyapustin et al, 2014), but larger discrepancies between calibrated Aqua and Terra measurements have been observed in the most recent data (post 2014) (Casey et al, 2017). MODIS C6 data have been shown to be capable of identifying trends in surface albedo >0.01 decade -1 (Lyapustin et al, 2014).…”

“…A recent analysis of summer (June-August) ice surface albedo changes from MODIS C6 data identified statistically significant 115 declines in surface albedo over the wet snow zone of the Greenland Ice Sheet during the period 2001-2016. For the most part, these decreases in surface albedo are thought to be physically real (Casey et al, 2017).…”

Modelling the climate and surface mass balance of polar ice sheets using RACMO2 – Part 1: Greenland (1958–2016)

“…Mixed reflectance from bright ice cover (∼ 0.55) and neighbouring darker tundra, exposed nunataks or meltwater ponds (< 0.30), located within the same MODIS grid cell, likely explains this underestimation. Another explanation stems from the deterioration of MODIS sensors in time, resulting in underestimated surface albedo records for the MCD43A3v5 product (Polashenski et al, 2015;Casey et al, 2017). LW n is well reproduced in the model due to similar negative biases in LW d and LW u (∼ 12 W m −2 ), again indicating underestimated cloud cover.…”