The advanced baseline imager (ABI) on board geostationary operational environmental satellite-16 (GOES-16) provides high quality reflective solar band (RSB) and thermal emission band (TEB) image data. Intensive field campaigns for postlaunch validation of the ABI Level-1B spectral radiance observations were carried out during March to May of 2017 to ensure the Système International traceability of the ABI. Radiometric calibrations of the RSBs and TEBs of the ABI were evaluated by comparison with the spectral measurements of the airborne visible infrared imaging spectrometer-next generation (AVIRIS-NG) and scanning high-resolution interferometer sounder (S-HIS) on board the high-altitude aircraft ER2, respectively. The comparison between ABI RSB mesoscale (MESO) data and AVIRIS-NG measurements showed that the mean biases are within 2% with uncertainty <2.5 % for ABI CH01, CH03, CH05, and CH06. The brightness temperature differences between GOES-16 ABI and S-HIS measurements were shown to be within 0.45 K with uncertainty <0.35 K at the 300 K scene equivalent for ABI CH08 to CH10 and CH13 to CH15. The ABI uses large focal plane arrays with the detector number varying from hundreds to more than a thousand per channel, which makes the evaluation of detector uniformity a challenge. Reanalysis of the GOES-16 ABI north-south scan data from the field campaign and lunar observation was performed for ABI CH01 to CH03 with two versions of calibration coefficients. Significant improvements in detector uniformity with the updated solar calibration algorithm were verified.