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Validation of TES ammonia observations at the single pixel scale in the San Joaquin Valley during DISCOVER‐AQ
Author(s) -
Sun Kang,
CadyPereira Karen,
Miller David J.,
Tao Lei,
Zondlo Mark A.,
Nowak John B.,
Neuman J. A.,
Mikoviny Tomas,
Müller Markus,
Wisthaler Armin,
Scarino Amy J.,
Hostetler Chris A.
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd022846
Subject(s) - transect , san joaquin , remote sensing , in situ , footprint , environmental science , troposphere , mixing ratio , image resolution , atmospheric sciences , geology , meteorology , soil science , optics , physics , paleontology , oceanography
Ammonia measurements from a vehicle‐based, mobile open‐path sensor and those from aircraft were compared with Tropospheric Emission Spectrometer (TES) NH 3 columns at the pixel scale during the NASA Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality field experiment. Spatial and temporal mismatches were reduced by having the mobile laboratory sample in the same areas as the TES footprints. To examine how large heterogeneities in the NH 3 surface mixing ratios may affect validation, a detailed spatial survey was performed within a single TES footprint around the overpass time. The TES total NH 3 column above a single footprint showed excellent agreement with the in situ total column constructed from surface measurements with a difference of 2% (within the combined measurement uncertainties). The comparison was then extended to a TES transect of nine footprints where aircraft data (5–80 ppbv) were available in a narrow spatiotemporal window (<10 km, <1 h). The TES total NH 3 columns above the nine footprints agreed to within 6% of the in situ total columns derived from the aircraft‐based measurements. Finally, to examine how TES captures surface spatial gradients at the interpixel scale, ground‐based, mobile measurements were performed directly underneath a TES transect, covering nine footprints within ±1.5 h of the overpass. The TES total columns were strongly correlated ( R 2 = 0.82) with the median NH 3 mixing ratios measured at the surface. These results provide the first in situ validation of the TES total NH 3 column product, and the methodology is applicable to other satellite observations of short‐lived species at the pixel scale.