Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and CH4, from space. The GOSAT carries a Fourier transform spectrometer and a push broom imager. The development of GOSAT satellite and sensors has almost finished after the characterization of sensor performance in laboratory. In orbit, the observation data will be evaluated by onboard calibration data and implemented by ground processing system. Level 1 algorithm and processing system are developed by JAXA. The post-launch calibration items are planned and the methods are developed before launching. We show the Level 1 processing and in-orbit calibration of GOSAT sensors.
Abstract. We describe a method for removing systematic biases of column-averaged dry air mole fractions of CO2 (XCO2) and CH4 (XCH4) derived from short-wavelength infrared (SWIR) spectra of the Greenhouse gases Observing SATellite (GOSAT). We conduct correlation analyses between the GOSAT biases and simultaneously retrieved auxiliary parameters. We use these correlations to bias correct the GOSAT data, removing these spurious correlations. Data from the Total Carbon Column Observing Network (TCCON) were used as reference values for this regression analysis. To evaluate the effectiveness of this correction method, the uncorrected/corrected GOSAT data were compared to independent XCO2 and XCH4 data derived from aircraft measurements taken for the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project, the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the Japan Meteorological Agency (JMA), the HIAPER Pole-to-Pole observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. These comparisons demonstrate that the empirically derived bias correction improves the agreement between GOSAT XCO2/XCH4 and the aircraft data. Finally, we present spatial distributions and temporal variations of the derived GOSAT biases.
Pronounced enhancements of total and tropospheric ozone were observed with the Brewer spectrophotometer and ozonesondes at Watukosek (7.5°S, 112.6°E), Indonesia in 1994 and in 1997 when extensive forest fires were reported in Indonesia. The integrated tropospheric ozone increased from 20 DU to 40 DU in October 1994 and to 55 DU in October 1997. On October 13, 1994, most ozone mixing ratios were more than 50 ppbv throughout the troposphere and exceeded 80 ppbv at some altitudes. On October 22, 1997, the concentrations were more than 50 ppbv throughout the troposphere and exceeded 100 ppbv at several altitudes. The coincidences of the ozone enhancements with the forest fires suggest the photochemical production of tropospheric ozone due to its precursors emitted from the fires for both cases. The years of 1994 and 1997 correspond to El Niño events when convective activity becomes low in Indonesia. Thus, in this region, it is likely that pronounced enhancements of tropospheric ozone associated with extensive forest fires due to sparse precipitation may take place with a period of a few years coinciding with El Niño events. This is in a marked contrast to the situation in South America and Africa where large‐scale biomass burnings occur every year.
Measurements of NO and NO y were carried out during NASA's Pacific Exploratory Mission‐West A. In total, 18 aircraft flights were made over the Pacific Ocean, predominantly over the western Pacific Ocean in September and October 1991. NO and NO y were measured using a chemiluminescence instrument, and NO x was calculated from NO using a chemical box model. The measurements were carried out from 0.3 to 12 km in altitude. The NO, calculated NO x ((NO x ) mc ), and NO y mixing ratios in continental air were significantly higher than in maritime air. In maritime air, NO increased with altitude. The median values of NO in the boundary layer and the lower, middle, and upper troposphere were 3.7, 5.1, 11.5, and 26.6 parts per trillion by volume (pptv), respectively. In continental air, NO and (NO x ) mc mixing ratios revealed a C‐shaped profile. The median NO y values observed in the four altitude regions were 37.8, 17.5, 18.2, and 53.2 pptv, respectively. NO y did not show any apparent altitude dependence either in maritime or in continental air. In maritime air, median NO y , values in the lower, middle, and upper troposphere ranged between 211 and 226 pptv and in continental air between 382 and 401 pptv. The lowest values of NO y , PAN, and O 3 were observed in tropical air masses throughout the entire altitude region. In the middle and upper troposphere of the high‐latitude air masses, NO and (NO x ) mc values were the lowest, although NO y mixing ratios were similar to those in continental air masses. PAN, O 3 , CO, CH 4 , and C 2 H 6 data were used to study the budget of reactive nitrogen over the Pacific Ocean. O 3 mixing ratios were found to be correlated with those of (NO x ) mc , NO y , PAN, and CH 4 , although the degree of correlation varied with air mass and altitude. These correlations, together with the profiles of these species, suggest that photochemical production of O 3 from precursor species over the continent is important for the O 3 budget in the troposphere over the western Pacific Ocean.
Measurements of NO, NO y , PAN, HNO 3 , O 3 , CO, CH 4 , nonmethane hydrocarbons (NMHCs), and H 2 O were made over the Pacific Ocean in February and March during the Pacific Exploratory Mission West B (PEM‐West B). NO x , was calculated from NO using a photochemical model. These data were classified according to six air mass categories: western Pacific maritime, tropical, tropical convective, western Pacific continental, high latitude, and stratospheric. It has been found that the mixing ratios of many of the observed species and partitioning of NO y varied significantly depending on altitude, air mass, and season. These variations have been interpreted in terms of chemical and transport processes. In the maritime air below 7 km, the mixing ratios of calculated NO x ((NO x ) mc ), PAN, and NO y were lower than those in the continental air masses. The lowest values of PAN, HNO 3 , NO y , and O 3 were observed in the tropical region below 5 km. In the continental air, NO y , PAN, CO, and NMHC levels below 4 km were much higher than those obtained in September and October during PEM‐West A, due to rapid transport of these species from anthropogenic sources on the continent to the Pacific Ocean by the westerly winds which dominated in early winter and spring. Reduced photochemistry during winter also contributed to the higher values of CO and NMHCs. Above 7 km the values of these species were lower during PEM‐West B, possibly due to much weaker convective activity in early spring. In spite of the weaker vertical transport, the median values of (NO x ) mc and the (NO x ) mc /C 3 H 8 ratio at 10 km were 110–140 parts per trillion by volume (pptv) and 2.9–3.4 pptv/pptv, respectively, in the continental and maritime air masses, indicating the importance of in situ NO x production in the upper troposphere. In the continental air the PAN/NO y and HNO 3 /NO y ratios ranged between 0.2 and 0.5, showing clear anticorrelation. The PAN/NO y ratio was also anticorrelated with the temperature. In the high‐latitude air between 1 and 7 km the PAN/NO 3 , ratio was 0.5–0.8, and the (NO x ) mc /NO y ratio was less than 0.05. Temperature and the concentrations of OH and NMHCs are considered to have strongly influenced the partitioning of NO y at middle and high latitudes. Generally, the sum of (NO x ) mc , PAN, and HNO 3 constituted 90±10% of the observed NO y from the boundary layer up to 7 km in all types of air masses. This finding improves our basic understanding on the chemistry and budget of the reactive nitrogen.
Validation of the Measurements of Pollution in the Troposphere (MOPITT) retrievals of carbon monoxide (CO) has been performed with a varied set of correlative data. These include in situ observations from a regular program of aircraft observations at five sites ranging from the Arctic to the tropical South Pacific Ocean. Additional in situ profiles are available from several short‐term research campaigns situated over North and South America, Africa, and the North and South Pacific Oceans. These correlative measurements are a crucial component of the validation of the retrieved CO profiles and columns from MOPITT. The current validation results indicate good quantitative agreement between MOPITT and in situ profiles, with an average bias less than 20 ppbv at all levels. Comparisons with measurements that were timed to sample profiles coincident with MOPITT overpasses show much less variability in the biases than those made by various groups as part of research field experiments. The validation results vary somewhat with location, as well as a change in the bias between the Phase 1 and Phase 2 retrievals (before and after a change in the instrument configuration due to a cooler failure). During Phase 1, a positive bias is found in the lower troposphere at cleaner locations, such as over the Pacific Ocean, with smaller biases at continental sites. However, the Phase 2 CO retrievals show a negative bias at the Pacific Ocean sites. These validation comparisons provide critical assessments of the retrievals and will be used, in conjunction with ongoing improvements to the retrieval algorithms, to further reduce the retrieval biases in future data versions.
The Biomass Burning and Lightning Experiment (BIBLE) A and B campaigns over the tropical western Pacific during springtime deployed a Gulfstream‐II aircraft with systems to measure ozone and numerous precursor species. Aerosol measuring systems included a MASP optical particle counter, a condensation nucleus (CN) counter, and an absorption spectrometer for black carbon. Aerosol volume was very low in the middle and upper troposphere during both campaigns, and during BIBLE A, there was little aerosol enhancement in the boundary layer away from urban areas. In BIBLE B, there was marked aerosol enhancement in the lowest 3 km of the atmosphere. Mixing ratios of CN in cloud‐free conditions in the upper troposphere were in general higher than in the boundary layer, indicating new particle formation from gaseous precursors. High concentrations of black carbon were observed during BIBLE B, with mass loadings up to 40 μg m −3 representing as much as one quarter of total aerosol mass. Strong correlations with hydrocarbon enhancement allow the determination of a black carbon emission ratio for the fires at that time. Expressed as elemental carbon, it is about 0.5% of carbon dioxide and 6% of carbon monoxide emissions from the same fires, comparable to methane production, and greater than that of other hydrocarbons.
