242 research outputs found
Performance study and analysis method for a new-generation MIPAS experiment
No full textThis study fits within the ongoing activities aimed at filling the lack of an operational IR limb sounder after the ENVISAT fault. Notably, we report the performance of a possible evolution of the MIPAS experiment. The strategy proposed for the new experiment (that we denote as MIPAS2k) is derived from the PREMIER infrared limb sounder (IRLS) and relies on both 1D array detector technology and reduction of the spectral resolution to achieve dense atmospheric sampling. We define observation parameters and report, as an example, the performance obtained by MIPAS2k when measuring O3 fields. The information load (IL) analysis was exploited to assess the sensitivity of MIPAS2k and to select optimal spectral intervals for retrieval tests on simulated observations of the new experiment. The results of the IL analysis suggest a new approach to the retrieval strategy (denoted as full-2D) in which the unknown parameter is no longer an element of the altitude profile but the constant value taken by the atmospheric quantity within a parcel (denoted as “clove”) of the 2D discretization. We demonstrate that the clove homogeneity assumption generates errors that are below the spectral noise of MIPAS2k when an appropriate clove thickness is used. Full-2D retrievals have been carried out on MIPAS2k simulated observations corresponding to a high resolution model atmosphere. We report a test case on O3 VMR in which the retrieval precision is better than 5% between 20 and 40 km and better than 30% in the upper troposphere-lower stratosphere. We test the ability of MIPAS2k to reconstruct a fine O3 structure present in the model atmosphere and we show how this structure would have been represented by MIPAS when measuring the same scenario. We have estimated the spatial resolution of MIPAS2k products by means of the perturbation approach that, in simulated retrievals, can be adopted to evaluate the averaging kernel of the retrieval parameters. For O3 we have found the estimates of 200 km and 2.5 km for the horizontal and vertical resolutions respectively
A strategy for the measurement of CO<sub>2</sub> distribution in the stratosphere
No full textIn this study we introduce a new strategy for the measurement of CO2
distribution in the stratosphere. The proposed experiment is based on an
orbiting limb sounder that measures the atmospheric emission within both the
thermal infrared (TIR) and far-infrared (FIR) regions. The idea is to exploit
the contribution of the pure rotational transitions of molecular oxygen in
the FIR to determine the atmospheric fields of temperature and pressure that
are necessary to retrieve the distribution of CO2 from its rovibrational transitions in the TIR. The instrument envisaged to test the new strategy is a
Fourier transform spectrometer with two output ports hosting a FIR detector
devoted to measuring the O2 transitions and a TIR detector devoted to
measure the CO2 transitions. Instrumental and observational parameters
of the proposed experiment have been defined by exploiting the heritage of
both previous studies and operational limb sounders. The performance of the
experiment has been assessed with two-dimensional (2-D)
retrievals on simulated observations
along a full orbit. For this purpose, optimal spectral intervals have been
defined using a validated selection algorithm. Both precision and spatial
resolution of the obtained CO2 distributions have been taken into
account in the results–evaluation process. We show that the O2 spectral
features significantly contribute to the performance of CO2 retrievals
and that the proposed experiment can determine 2-D distributions of the
CO2 volume mixing ratio with precisions of the order of 1 ppmv in the
10–50 km altitude range. The error budget, estimated for the test case of
an ideal instrument and neglecting the spectroscopic errors, indicates that,
in the 10–50 km altitude range, the total error of the CO2 fields is
set by the random component. This is also the case at higher altitudes,
provided the retrieval system is able to model the non-local thermal
equilibrium conditions of the atmosphere. The best
performance is obtained at altitudes between 20 and 50 km, where the
vertical resolution ranges from 3 to 5 km, and the horizontal resolution is
of the order of 300–350 km depending on latitude
Assessment of the impact of the systematic errors on the retrieval of geophysical parameters from FORUM measurements: methods and results
No full text
Comparison of measurements made with two different instruments of the same atmospheric vertical profile
No full textPhosgene in the UTLS: seasonal and latitudinal variations from MIPAS observations
No full textThe Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a
Fourier transform spectrometer that measured mid-infrared atmospheric limb
emission spectra from July 2002 to April 2012 on board the polar-orbiting
satellite ENVISAT. We have used MIPAS data to study the latitudinal
variations of phosgene (COCl2 or carbonyl chloride) and, for the first time, its seasonal variation in the upper troposphere/lower stratosphere
region (UTLS). Retrievals of phosgene were made using the 830–860 cm−1 region, corresponding to the ν5 bands of COCl2. Unfortunately, in that region, the ν4 band of CFC-11, which is much stronger than COCl2 ν5, hides the phosgene emission. In order to evaluate seasonality and latitudinal distribution of phosgene we have analysed all the measurements made by MIPAS on days 18 and 20 of each month of 2008 with the optimized retrieval
model (ORM) recently upgraded with the multi-target retrieval technique and
with the optimal estimation functionality to apply external constraints to
the state vector. Average seasonal profiles of phosgene show an evident
latitudinal variability with the largest values observed in the tropical
regions (maximum ≈ 35 parts per trillion by volume (pptv) at about
300 hPa). In the midlatitude and polar regions, the volume mixing ratio
(VMR) values do not exceed 30 pptv and the vertical distributions are less
peaked. Our analysis highlights that COCl2 seasonal variability is fairly low, apart from the polar regions
Bianca Garavelli studiosa e scrittrice
No full textBianca Garavelli (Vigevano, 1958-2021) was a highly regarded figure in the literary world, both on the critical and creative side. Author of important critical studies on Dante and of a successful commentary on the Commediam (begun under the supervision of Maria Corti but then continued independently), as well as critic and reviewer for newspapers and periodicals, Garavelli also wrote and published poems, novels and short stories. This article offers an exhaustive bio-bibliographical profile of Bianca Garavelli, whose literary work in various fields is reconstructed and critically examined
Errors induced by different approximations in handling horizontal atmospheric inhomogeneities in MIPAS/ENVISAT retrievals
No full textMIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a
mid-infrared limb emission sounder that operated on board the polar satellite
ENVISAT from 2002 to 2012. The retrieval algorithm used by the European Space
Agency to process MIPAS measurements exploits the assumption that the
atmosphere is horizontally homogeneous. However, previous studies highlighted
how this assumption causes significant errors on the retrieved profiles of
some MIPAS target species.In this paper we quantify the errors induced by this assumption and evaluate
the performances of three different algorithms that can be used to mitigate
the problem. We generate synthetic observations with a high spatial
resolution atmospheric model and carry out the retrievals with four
alternative methods. The first assumes horizontal homogeneity (1-D retrieval),
the second includes a model of the horizontal gradient of atmospheric
temperature (1-D plus temperature gradient retrieval), the third accounts for
an horizontal gradient of temperature and composition (1-D plus temperature
and composition gradient retrieval), while the fourth is the full
two-dimensional (2-D) inversion approach.Our results highlight that the 1-D retrieval implies errors that are
significant for averages of profiles. Furthermore, for some targets (e.g.
T, CH4 and N2O below 10 hPa) the error induced by the 1-D
approximation also becomes visible in the individual retrieved profiles. The
inclusion of any kind of horizontal variability model improves all the
targets with respect to the horizontal homogeneity assumption. For
temperature, HNO3 and CFC-11, the inclusion of an horizontal temperature
gradient leads to a significant reduction of the error. For other targets, such as
H2O, O3, N2O, CH4, the improvements due to the inclusion of an
horizontal temperature gradient are minor. In these cases, the inclusion of a
gradient in the target volume mixing ratio leads to significant improvements.
Among all the methods tested in this work, the 2-D approach, as expected,
implies the smallest errors for almost all the target parameters. This
residual error of the 2-D approach is the smoothing caused by the retrieval
grid, which is coarser than that of the atmospheric model
- …
