VALIDATION OF SCIAMACHY SCIENTIFIC RETRIEVALS OF CO, CH_4, N_2O, AND NO_2 BY FTIR AT THE GROUND TRUTHING STATION ZUGSPITZE

摘要

Solar FTIR measurements at the Permanent GroundrnTruthing Station Zugspitze (47 °N, 11 °E), Germanyrnare used to validate ENVISAT/SCIAMACHY ScientificrnData Products retrieved at the University of Bremen,rni.e., the infrared WFM-DOAS ver. 0.4 total columnrnproducts of CO, CH_4, N_2O, and the scientific DOASrnNO_2 column product (ver. UB1.0). For WFM-DOAS,rnonly relative changes due to the annual cycle arerninvestigated, since these column retrievals includernempirical scaling factors. To obtain a statisticallyrnsignificant fit to the CO annual cycle (≈10 % amplitude)rnout of the scatter of the SCIAMACHY WFM-DOASrndata (available data cover Jan-Oct 2003), all pixelsrnwithin a radius of at least 1000-2000 km aroundrnZugspitze had to be averaged for each day. The weakerrn(2.5 % amplitude) annual cycles of CH_4 and N_2O couldrnnot be retrieved from SCIAMACHY data, even usingrnaverages of all pixels within a full latitudinal band ofrn±2000 km north/south relative to the Zugspitze aroundrnthe globe. Validating one full year of UB1.0 NO_2 totalrncolumn data (Jul 2003 – Jun 2003) a perfect agreementrnof the annual cycle to the ground FTIR data has beenrnfound, after removing obvious enhancements due tornpollution episodes not captured by the high altitudern(2964 m asl.) Zugspitze FTIR. After this correction, thernSCIAMACHY UB1.0 columns of NO_2 are 16 % belowrnthe Zugspitze FTIR columns on average.