scholarly journals Assessment of global total column water vapor sounding using a spaceborne differential absorption radar

2020 ◽  
Author(s):  
Luis Millán ◽  
Richard Roy ◽  
Matthew Lebsock
Keyword(s):  
Water Vapor ◽  
Pulse Compression ◽  
Atmospheric Conditions ◽  
Differential Absorption ◽  
Ice Clouds ◽  
Scattering Effects ◽  
Vapor Line ◽  
The Tropics ◽  
Total Column ◽  
Better Than

Abstract. The feasibility of using a differential absorption radar (DAR) to retrieve total column water vapor from space is investigated. DAR combines at least two radar tones near an absorption line, in this case a water vapor line, to measure humidity information from the differential absorption on and off the line. From a spaceborne platform, DAR can be used to retrieve total column water vapor by measuring the differential reflection from the Earth's Surface. We assess the expected precision, yield, and potential biases of retrieved total column water vapor values by applying an end-to-end radar instrument simulator to near-global weather analysis fields collocated with CloudSat measurements. The approach allows us to characterize the DAR performance across a globally representative dataset of atmospheric conditions including clouds and precipitation as well as different surface types. We assume a hypothetical spaceborne G-band radar with pulse compression orbiting the earth at 405 km with a 1 m antenna, equivalent to a footprint diameter of 850 m, and 500 m horizontal integration. The simulations include the scattering effects of rain, snow, as well as liquid and ice clouds, spectroscopic uncertainties, and uncertainties due to the initial assumed water vapor profile. Results indicate that, using two radar tones at 167 and 174.8 GHz with a transmit power of 20 W ensures that both pulses will reach the surface at least 70 % of the time in the tropics and more than 90 % of the time outside the tropics, and that total column water vapor can be retrieved with a precision better than 1.3 mm.

scholarly journals Assessment of global total column water vapor sounding using a spaceborne differential absorption radar

2020 ◽  
Vol 13 (10) ◽  
pp. 5193-5205
Author(s):  
Luis Millán ◽  
Richard Roy ◽  
Matthew Lebsock
Keyword(s):  
Water Vapor ◽  
Pulse Compression ◽  
Signal To Noise Ratio ◽  
Atmospheric Conditions ◽  
Differential Absorption ◽  
Ice Clouds ◽  
Scattering Effects ◽  
The Tropics ◽  
Total Column ◽  
Better Than

Abstract. The feasibility of using a differential absorption radar (DAR) to retrieve total column water vapor from space is investigated. DAR combines at least two radar tones near an absorption line, in this case a water vapor line, to measure humidity information from the differential absorption “on” and “off” the line. From a spaceborne platform, DAR can be used to retrieve total column water vapor by measuring the differential reflection from the Earth's surface. We assess the expected precision, yield, and potential biases of retrieved total column water vapor values by applying an end-to-end radar instrument simulator to near-global weather analysis fields collocated with CloudSat measurements. The approach allows us to characterize the DAR performance across a globally representative dataset of atmospheric conditions including clouds and precipitation as well as different surface types. We assume a hypothetical spaceborne G-band radar with pulse compression orbiting the Earth at 405 km with a 1 m antenna, equivalent to a footprint diameter of 850, and 500 m horizontal integration. The simulations include the scattering effects of rain, snow, as well as liquid and ice clouds, spectroscopic uncertainties, and uncertainties due to the initial assumed water vapor profile. Results indicate that using two radar tones at 167 and 174.8 GHz with a transmit power of 20 W ensures that both pulses will be detected with a signal-to-noise ratio greater than 1 at least 70 % of the time in the tropics and more than 90 % of the time outside the tropics and that total column water vapor can be retrieved with a precision better than 1.3 mm.

scholarly journals Differential Absorption Radar Techniques: Water Vapor Retrievals

2016 ◽  
Author(s):  
Luis Millan ◽  
Matthew Lebsock ◽  
Nathaniel Livesey ◽  
Simone Tanelli
Keyword(s):  
Water Vapor ◽  
Horizontal Resolution ◽  
Differential Absorption ◽  
Vapor Line ◽  
End To End ◽  
Total Column

Abstract. Two radar pulses sent at different frequencies near the 183 GHz water vapor line can be used to determine total column water vapor and water vapor profiles (within clouds or precipitation) exploiting the differential absorption on and off the line. We asses these water vapor measurements by applying a radar instrument simulator to CloudSat pixels and then, running end-to-end retrieval simulations. These end-to-end retrievals enable us to fully characterize not only the expected precision but also their potential biases, allowing us to select radar tones that maximize the water vapor signal minimizing potential errors due to spectral variations in the target extinction properties. A hypothetical CloudSat-like instrument with 500m by ~1 km vertical and horizontal resolution and a minimum detectable signal and radar precision of −30 dBZ and 0.16 dBZ, respectively, can estimate total column water vapor with an expected precision of around 0.03 cm with potential biases most of the time smaller than 0.26 cm, even under rainy conditions. The expected precision for water vapor profiles was found to be on average around 89 % with potential biases most of the time smaller than 77 % when the profile is being retrieved close to surface but smaller than 38 % above 3 km. By using either horizontal or vertical averaging, the precision will improve vastly with the measurements still retaining a considerably high vertical and/or horizontal resolution.

scholarly journals Differential absorption radar techniques: water vapor retrievals

2016 ◽  
Vol 9 (6) ◽  
pp. 2633-2646 ◽  
Author(s):  
Luis Millán ◽  
Matthew Lebsock ◽  
Nathaniel Livesey ◽  
Simone Tanelli
Keyword(s):  
Water Vapor ◽  
Horizontal Resolution ◽  
Differential Absorption ◽  
Vapor Line ◽  
End To End ◽  
Total Column

Abstract. Two radar pulses sent at different frequencies near the 183 GHz water vapor line can be used to determine total column water vapor and water vapor profiles (within clouds or precipitation) exploiting the differential absorption on and off the line. We assess these water vapor measurements by applying a radar instrument simulator to CloudSat pixels and then running end-to-end retrieval simulations. These end-to-end retrievals enable us to fully characterize not only the expected precision but also their potential biases, allowing us to select radar tones that maximize the water vapor signal minimizing potential errors due to spectral variations in the target extinction properties. A hypothetical CloudSat-like instrument with 500 m by  ∼  1 km vertical and horizontal resolution and a minimum detectable signal and radar precision of −30 and 0.16 dBZ, respectively, can estimate total column water vapor with an expected precision of around 0.03 cm, with potential biases smaller than 0.26 cm most of the time, even under rainy conditions. The expected precision for water vapor profiles was found to be around 89 % on average, with potential biases smaller than 77 % most of the time when the profile is being retrieved close to surface but smaller than 38 % above 3 km. By using either horizontal or vertical averaging, the precision will improve vastly, with the measurements still retaining a considerably high vertical and/or horizontal resolution.

scholarly journals Differential absorption lidar measurements of water vapor by the High Altitude Lidar Observatory (HALO): Retrieval framework and validation

2021 ◽  
Author(s):  
Brian J. Carroll ◽  
Amin R. Nehrir ◽  
Susan Kooi ◽  
James Collins ◽  
Rory A. Barton-Grimley ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Altitude ◽  
Dynamic Range ◽  
Precipitable Water ◽  
Spatiotemporal Variability ◽  
High Spectral Resolution ◽  
Atmospheric Conditions ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
Wide Range

Abstract. Airborne differential absorption lidar (DIAL) offers a uniquely capable solution to the problem of measuring water vapor (WV) with high precision, accuracy, and resolution throughout the troposphere and lower stratosphere. The High Altitude Lidar Observatory (HALO) airborne WV DIAL was recently developed at NASA Langley Research Center and was first deployed in 2019. It uses four wavelengths at 935 nm to achieve sensitivity over a wide dynamic range, and simultaneously employs 1064 nm backscatter and 532 nm high spectral resolution lidar (HSRL) measurements for aerosol and cloud profiling. A key component of the WV retrieval framework is flexibly trading resolution for precision to achieve optimal data sets for scientific objectives across scales. A technique for retrieving WV in the lowest few hundred meters of the atmosphere using the strong surface return signal is also presented. The five maiden flights of the HALO WV DIAL spanned the tropics through midlatitudes with a wide range of atmospheric conditions, but opportunities for validation were sparse. Comparisons to dropsonde WV profiles were qualitatively in good agreement, though statistical analysis was impossible due to systematic error in the dropsonde measurements. Comparison of HALO to in situ WV measurements onboard the aircraft showed no substantial bias across three orders of magnitude, despite variance (R2 = 0.66) that may be largely attributed to spatiotemporal variability. Precipitable water vapor measurements from the spaceborne sounders AIRS and IASI compared very well to HALO with R2 > 0.96 over ocean and R2 = 0.86 over land.

scholarly journals Field-deployable diode-laser-based differential absorption lidar (DIAL) for profiling water vapor

2015 ◽  
Vol 8 (3) ◽  
pp. 1073-1087 ◽  
Author(s):  
S. M. Spuler ◽  
K. S. Repasky ◽  
B. Morley ◽  
D. Moen ◽  
M. Hayman ◽  
...  
Keyword(s):  
Water Vapor ◽  
Diode Laser ◽  
Temporal Resolution ◽  
Filter Design ◽  
Wide Field ◽  
Atmospheric Conditions ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
Atmospheric Sciences ◽  
Range Resolution

Abstract. A field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested. Significant advances are discussed, including a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with optomechanical and thermal stability; multistage optical filtering enabling measurement during daytime bright-cloud conditions; rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions; and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing, and intercomparisons are performed and discussed. In general, the instrument has a 150 m range resolution with a 10 min temporal resolution; 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument is shown capable of autonomous long-term field operation – 50 days with a > 95% uptime – under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.

scholarly journals A climatology of formation conditions for aerodynamic contrails

2013 ◽  
Vol 13 (21) ◽  
pp. 10847-10857 ◽  
Author(s):  
K. Gierens ◽  
F. Dilger
Keyword(s):  
Climate Impact ◽  
Reanalysis Data ◽  
Air Traffic ◽  
Liquid Droplets ◽  
Atmospheric Conditions ◽  
Climate Effect ◽  
Ice Clouds ◽  
Formation Conditions ◽  
The Tropics ◽  
Global Reanalysis

Abstract. Aircraft at cruise levels can cause two kinds of contrails, the well known exhaust contrails and the less well-known aerodynamic contrails. While the possible climate impact of exhaust contrails has been studied for many years, research on aerodynamic contrails began only a few years ago and nothing is known about a possible contribution of these ice clouds to climate impact. In order to make progress in this respect, we first need a climatology of their formation conditions and this is given in the present paper. Aerodynamic contrails are defined here as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data: first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Furthermore, we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally, we argue that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

scholarly journals Field deployable diode-laser-based differential absorption lidar (DIAL) for profiling water vapor

2014 ◽  
Vol 7 (11) ◽  
pp. 11265-11302 ◽  
Author(s):  
S. M. Spuler ◽  
K. S. Repasky ◽  
B. Morley ◽  
D. Moen ◽  
M. Hayman ◽  
...  
Keyword(s):  
Water Vapor ◽  
Diode Laser ◽  
Temporal Resolution ◽  
Filter Design ◽  
Wide Field ◽  
Atmospheric Conditions ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
Atmospheric Sciences ◽  
Range Resolution

Abstract. A field deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes has been constructed and tested. Significant advances are discussed, including: a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with opto-mechanical and thermal stability, multi-stage optical filtering enabling measurement during daytime bright-cloud conditions, rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions, and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing and intercomparisons have been performed and are discussed. In general, the instrument has 150 m range resolution with 10 min temporal resolution – 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument was shown capable of autonomous long term field operation – 50 days with a >95% uptime – under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.

scholarly journals Intercomparison of atmospheric water vapor soundings from the differential absorption lidar (DIAL) and the solar FTIR system on Mt. Zugspitze

2011 ◽  
Vol 4 (5) ◽  
pp. 835-841 ◽  
Author(s):  
H. Vogelmann ◽  
R. Sussmann ◽  
T. Trickl ◽  
T. Borsdorff
Keyword(s):  
Water Vapor ◽  
Near Infrared ◽  
Integration Time ◽  
Research Station ◽  
Horizontal Distance ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
The Mean ◽  
The Difference ◽  
Better Than

Abstract. We present an intercomparison of three years of measurements of integrated water vapor (IWV) performed by the mid-infrared solar FTIR (Fourier Transform Infra-Red) instrument on the summit of Mt. Zugspitze (2964 m a.s.l.) and by the nearby near-infrared differential absorption lidar (DIAL) at the Schneefernerhaus research station (2675 m a.s.l.). The solar FTIR was shown to be one of the most accurate and precise IWV sounders in recent work (Sussmann et al., 2009) and is taken as the reference here. By calculating the FTIR-DIAL correlation (22 min coincidence interval, 15 min integration time) we derive an almost ideal slope of 0.996 (10), a correlation coefficient of R = 0.99, an IWV intercept of −0.039 (42) mm (−1.2 % of the mean), and a bias of −0.052 (26) mm (−1.6 % of the mean) from the scatter plot. By selecting a subset of coincidences with an optimum temporal and spatial matching between DIAL and FTIR, we obtain a conservative estimate of the precision of the DIAL in measuring IWV which is better than 0.1 mm (3.2 % of the mean). We found that for a temporal coincidence interval of 22 min the difference in IWV measured by these two systems is dominated by the volume mismatch (horizontal distance: 680 m). The outcome from this paper is twofold: (1) the IWV soundings by FTIR and DIAL agree very well in spite of the differing wavelength regions with different spectroscopic line parameters and retrieval algorithms used. (2) In order to derive an estimate of the precision of state-of-the-art IWV sounders from intercomparison experiments, it is necessary to use a temporal matching on time scales shorter than 10 min and a spatial matching on the 100-m scale.

scholarly journals Intercomparison of atmospheric water vapor soundings from the differential absorption lidar (DIAL) and the solar FTIR system on Mt. Zugspitze

2010 ◽  
Vol 3 (6) ◽  
pp. 5411-5428 ◽  
Author(s):  
H. Vogelmann ◽  
R. Sussmann ◽  
T. Trickl ◽  
T. Borsdorff
Keyword(s):  
Water Vapor ◽  
Near Infrared ◽  
Integration Time ◽  
Research Station ◽  
Horizontal Distance ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
The Mean ◽  
The Difference ◽  
Better Than

Abstract. We present an intercomparison of three years of measurements of integrated water vapor (IWV) performed by the mid-infrared solar FTIR instrument on the summit of Mt. Zugspitze (2964 m a.s.l.) and the nearby near-infrared differential absorption lidar (DIAL) at the Schneefernerhaus research station (UFS, 2675 m a.s.l.). The solar FTIR turned out to be one of the most accurate and precise IWV sounders in recent work (Sussmann et al., 2009) and is taken as the reference here. By calculating the FTIR-DIAL correlation (22 min coincidence interval, 15 min integration time) we derive an almost ideal slope of 0.99(1), a correlation coefficient of R = 0.99, an IWV intercept of 0.056(42) mm (1.8% of the mean), and a bias of 0.097(26) mm (3.1% of the mean) from the scatter plot. By selecting a subset of coincidences with an optimum temporal and spatial matching between DIAL and FTIR, we obtain a conservative estimate of the precision of the DIAL in measuring IWV which is better than 0.1 mm (3.2% of the mean). We found that for a temporal coincidence interval of 22 min the difference in IWV measured by these two systems is dominated by the volume mismatch (horizontal distance: 680 m). The outcome from this paper is twofold: (1) The IWV soundings by FTIR and DIAL agree very well in spite of the differing wavelength regions with different spectroscopic line parameters and retrieval algorithms used. (2) In order to derive an estimate of the precision of state-of-the-art IWV sounders from intercomparison experiments, it is necessary to use a temporal matching on the shorter 10-min scale and a spatial matching on the smaller 1-km scale.

scholarly journals A climatology of formation conditions for aerodynamic contrails

2013 ◽  
Vol 13 (6) ◽  
pp. 14667-14693
Author(s):  
K. Gierens ◽  
F. Dilger
Keyword(s):  
Reanalysis Data ◽  
Air Traffic ◽  
Liquid Droplets ◽  
Atmospheric Conditions ◽  
Climate Effect ◽  
Ice Clouds ◽  
Formation Conditions ◽  
The Tropics ◽  
Global Reanalysis ◽  
Special Case

Abstract. Aerodynamic contrails are defined in this paper as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data, first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Finally we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally we give an argument for our believe that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

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