The benefit of limb cloud imaging for infrared limb sounding of tropospheric trace gases

Adams, Susanne; Spang, R.; Preusse, Peter; Heinemann, Günther

doi:10.5194/amt-2-287-2009

Cited by 4 publications

(2 citation statements)

References 31 publications

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“…4 where the "true state" ADP is computed from ECMWF data and compared with the retrieved CTH and ADP, it would be better to raytrace the MIPAS limb paths through the horizontally high resolved cloud parameter fields of the nadir instrument and to estimate, for example, an effective limb CTH from the nadir CTHs along the LOS. A similar approach was successfully applied to global nadir BTR composites to create realistic high resolved fields of CTHs (Adams et al, 2009). The study quantified the benefit of limb cloud imaging for infrared limb sounding of tropospheric trace gases.…”

Section: A Concept On How To Compare Limb and Nadir Cloud Occurrencesmentioning

confidence: 99%

Fast cloud parameter retrievals of MIPAS/Envisat

Spang¹,

Arndt²,

Dudhia

et al. 2012

Atmos. Chem. Phys.

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123

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The infrared limb spectra of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Envisat satellite include detailed information on tropospheric clouds and polar stratospheric clouds (PSC). However, no consolidated cloud product is available for the scientific community. Here we describe a fast prototype processor for cloud parameter retrieval from MIPAS (MIPclouds). Retrieval of parameters such as cloud top height, temperature, and extinction are implemented, as well as retrieval of microphysical parameters, e.g. effective radius and the integrated quantities over the limb path (surface area density and volume density). MIPclouds classifies clouds as either liquid or ice cloud in the upper troposphere and polar stratospheric clouds types in the stratosphere based on statistical combinations of colour ratios and brightness temperature differences. Comparison of limb measurements of clouds with model results or cloud parameters from nadir looking instruments is often difficult due to different observation geometries. We therefore introduce a new concept, the limb-integrated surface area density path (ADP). By means of validation and radiative transfer calculations of realistic 2-D cloud fields as input for a blind test retrieval (BTR), we demonstrate that ADP is an extremely valuable parameter for future comparison with model data of ice water content, when applying limb integration (ray tracing) through the model fields. In addition, ADP is used for a more objective definition of detection thresholds of the applied detection methods. Based on BTR, a detection threshold of ADP = 107 μm2 cm−2 and an ice water content of 10−5 g m−3 is estimated, depending on the horizontal and vertical extent of the cloud. Intensive validation of the cloud detection methods shows that the limb-sounding MIPAS instrument has a sensitivity in detecting stratospheric and tropospheric clouds similar to that of space- and ground-based lidars, with a tendency for higher cloud top heights and consequently higher sensitivity for some of the MIPAS detection methods. For the high cloud amount (HCA, pressure levels below 440 hPa) on global scales the sensitivity of MIPAS is significantly greater than that of passive nadir viewers. This means that the high cloud fraction will be underestimated in the ISCCP dataset compared to the amount of high clouds deduced by MIPAS. Good correspondence in seasonal variability and geographical distribution of cloud occurrence and zonal means of cloud top height is found in a detailed comparison with a climatology for subvisible cirrus clouds from the Stratospheric Aerosol and Gas Experiment II (SAGE II) limb sounder. Overall, validation with various sensors shows the need to consider differences in sensitivity, and especially the viewing geometries and field-of-view size, to make the datasets comparable (e.g. applyin...

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Section: A Concept On How To Compare Limb and Nadir Cloud Occurrencesmentioning

confidence: 99%

Fast cloud parameter retrievals of MIPAS/Envisat

Spang¹,

Arndt²,

Dudhia

et al. 2012

Atmos. Chem. Phys.

Self Cite

123

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“…The one discussed in this paper, the "dynamics mode", is designed for unprecedented 3-D spatial sampling and is thereby optimised to resolve small and mesoscale atmospheric temperature and trace gas structures (e.g. Adams et al, 2009). The sampling is 0.5 km in the vertical direction, 25 km across track (in a 320 km swath), and 50 km in the along track direction.…”

Section: Introductionmentioning

confidence: 99%

Tomographic retrieval approach for mesoscale gravity wave observations by the PREMIER Infrared Limb-Sounder

Ungermann¹,

Hoffmann²,

Preusse³

et al. 2010

Atmos. Meas. Tech.

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Abstract. PREMIER is one of three candidates for ESA's 7th Earth Explorer mission that are currently undergoing feasibility studies. The main mission objective of PREMIER is to quantify processes controlling atmospheric composition in the mid/upper troposphere and lower stratosphere, a region of particular importance for climate change. To achieve this objective, PREMIER will employ the first satellite Fourier transform infrared limb-imager with a 2-D detector array combined with a millimetre-wave limb-sounder. The infrared limb-imager can be operated in a high spatial resolution mode ("dynamics mode") for observations of smallscale structures in atmospheric temperatures and trace gas fields with unprecedented 3-D sampling (0.5 km in the vertical direction, 50 km along track, 25 km across track). In this paper, a fast tomographic retrieval scheme is presented, which is designed to fully exploit the high-resolution radiance observations of the dynamics mode. Based on a detailed analysis of the "observational filter", we show that the dynamics mode provides unique information on global distributions of gravity waves (GW). The achievable vertical resolution for GW observations has values between the vertical sampling (0.5 km) of the dynamics mode and the vertical field of view (about 0.75 km). The horizontal across track resolution corresponds to the horizontal across track sampling of 25 km. Since the achievable along track horizontal resolution is about 70 km, the dynamics mode will provide GW limb-observations with a horizontal resolution comparable to nadir sounders. Compared to previous observations, PREMIER will therefore considerably extend the range of detectable GWs in terms of horizontal and vertical wavelength.

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New perspectives on gravity wave remote sensing by spaceborne infrared limb imaging

Preusse¹,

Schroeder²,

Hoffmann³

et al. 2009

Atmos. Meas. Tech.

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Abstract. Gravity wave (GW) remote sensing from space now has reached a stage of maturity that some first confinements for GW modeling can be deduced. This is in particular due to global distributions of absolute values of GW momentum flux from infrared limb sounders and due to 2-D maps of the horizontal wave field provided by nadir viewing instruments. The logical step forward is an infrared limb imager (ILI) which combines the good vertical resolution of limb sounding with horizontal mapping capabilities and provides 3-D images of the GW temperature structures. In this paper we investigate 1) how an ILI advances measurements of GW momentum flux, 2) which additional benefits are achieved by limb imaging of GWs, and 3) how an ILI compares to other GW momentum flux measurements, in-situ, ground-based, and from space. In particular, the large advance made by gaining regular 3-D sampling is demonstrated.

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The benefit of limb cloud imaging for infrared limb sounding of tropospheric trace gases

Cited by 4 publications

References 31 publications

Fast cloud parameter retrievals of MIPAS/Envisat

Fast cloud parameter retrievals of MIPAS/Envisat

Tomographic retrieval approach for mesoscale gravity wave observations by the PREMIER Infrared Limb-Sounder

New perspectives on gravity wave remote sensing by spaceborne infrared limb imaging

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