Orbital variations and impacts on observations from SNPP, NOAA 18-20, and AQUA sun-synchronous satellites

Abstract

The AQUA, SNPP, and NOAA 18-20 PM sun-synchronous satellites were designed with similar local time, local solar zenith angles, and overlapping temporal coverage. Although the satellites are expected to have fixed local equatorcrossing time, during the satellite lifetime, the equator-crossing times of these satellites drift. For NOAA 18-19, the drift in equator-crossing time is significant (few hours) and no correction has been done over the lifetime. For SNPP and AQUA, correction in the orbital inclination angle was periodically performed to maintain the equator-crossing time around the designed value. The impact of systematic drift of the local observation time during the satellite life cycle can be significant and should be accounted for when using multi-year time series of satellite products in long-term environmental studies. In this paper, the equator-crossing time drift of AQUA, SNPP, and NOAA 18-20, the correction of SNPP and AQUA equator-crossing time via orbital inclination angle change, and the consequent local solar zenith angle variation are evaluated. The impact of such drift on low-latitude mean brightness temperature trend derived from the similar ~11 µm thermal emissive channel of AQUA MODIS CH31, SNPP Visible Infrared Imaging Radiometer Suite (VIIRS) CH15 and NOAA 18-19 HIRS CH08 are analyzed. The drift in the mean brightness temperature measured by these sensors is combined as a function of local time and analyzed using diurnal cycle analysis. The mean brightness temperature drift for SNPP VIIRS is reconciled within the context of much larger temperature drift of NOAA 18-19.

The Reprocessed Suomi NPP Satellite Observations

“…In addition, the S-NPP orbits drifted relative to Aqua in a zigzag pattern with a maximum of 10 min apart and a minimum near zero minute occurred in late 2014. This small orbital drift caused biases on the order of 0.03-0.08 K between the two instruments [93]. approximately 0.15 K than MODIS on average for both daytime and nighttime observations.…”

“…In addition, the S-NPP orbits drifted relative to Aqua in a zigzag pattern with a maximum of 10 min apart and a minimum near zero minute occurred in late 2014. This small orbital drift caused biases on the order of 0.03-0.08 K between the two instruments [93]. Trends for the VIIRS minus MODIS time series are 0.0165 ± 0.0119 K/Year for daytime passes and 0.0016 ± 0.0133 K/Year for nighttime passes, respectively, during the five years from January 2012 to March 2017, with VIIRS being warmer.…”

“…This is most likely related to diurnal drift difference. Shao et al [93] showed that the VIIRS M15 band was 0.084 K warmer than the MODIS B31 band in daytime passes in low latitudes, caused by the 10-min orbital drift of VIIRS relative to Aqua and a steeper temperature diurnal gradient near 1:30 pm local time. In contrast, orbital-drift related differences between the same two instrument bands were only of 0.028 K for nighttime passes due to a flat temperature diurnal gradient near 1:30 am local time [93], although orbital drift is also of 10-min magnitude between the two satellites.…”

Calibrating Geosynchronous and Polar Orbiting Satellites: Sharing Best Practices

“…If the follow-on sensors are in the same LECT orbit, the empirical BRDF from the previous sensor can be used to track the stability of the later one soon after launch [18]. Sensors in degrading orbits have been inter-calibrated, but the uncertainty of the inter-calibration increases significantly as the orbits drift toward the terminator [19][20][21][22].…”

An Ongoing Blended Long-Term Vegetation Health Product for Monitoring Global Food Security

“…[59]. It is worth emphasizing that the inclination angle of VIIRS on-board satellites have been periodically adjusted to maintain their equator crossing time around the designed value [60], so VIIRS experiences minimal drift. Further, due to no mega scale volcano eruption (such as El Chichon or Mt Pinatubo) yet in the VIIRS era, much fewer efforts are needed for noise correction of lower level products, compared to those in the AVHRR era.…”