A new algorithm for detecting cloud height using OMPS/LP measurements

Abstract. The Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) ozone product requires the determination of cloud height for each event to establish the lower boundary of the profile for the retrieval algorithm. We have created a revised cloud detection algorithm for LP measurements that uses the spectral dependence of the vertical gradient in radiance between two wavelengths in the visible and near-IR spectral regions. This approach provides better discrimination between clouds and aerosols than results obtained using a single wavelength. Observed LP cloud height values show good agreement with coincident Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements.

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A new algorithm for detecting cloud height using OMPS/LP measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-9-1239-2016 ◽

2016 ◽

Vol 9 (3) ◽

pp. 1239-1246 ◽

Cited By ~ 9

Author(s):

Zhong Chen ◽

Matthew DeLand ◽

Pawan K. Bhartia

Keyword(s):

Lower Boundary ◽

Vertical Gradient ◽

Satellite Observation ◽

Detection Algorithm ◽

Retrieval Algorithm ◽

Cloud Detection ◽

Near Ir ◽

Cloud Height ◽

Good Agreement

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Typhoon Warm-Core Structures Derived from FY-3D MWTS-2 Observations

Remote Sensing ◽

10.3390/rs13183730 ◽

2021 ◽

Vol 13 (18) ◽

pp. 3730

Author(s):

Zeyi Niu ◽

Xiaolei Zou ◽

Wei Huang

Keyword(s):

Linear Regression ◽

Multiple Linear Regression ◽

Three Dimensional ◽

Detection Algorithm ◽

Maximum Temperature ◽

Retrieval Algorithm ◽

Northwest Pacific ◽

Cloud Detection ◽

Warm Core ◽

Mean Square Errors

In this study, the three-dimensional (3D) warm-core structures of the Northwest Pacific typhoons Francisco, Lekima, and Krosa in August 2019 are retrieved from the Fengyun-3D (FY-3D) microwave temperature sounder-2 (MWTS-2) observations of brightness temperature. Due to the lack of two window channels at 23.8 GHz and 31.4 GHz, an empirical cloud detection algorithm based on 50.3 GHz bias-corrected observations-minus-backgrounds is applied to obtain clear-sky observations for the multiple linear regression retrieval algorithm. The MWTS-2 cloud-affected channels 3–5 are not used to retrieve temperatures under cloudy conditions to eliminate low-tropospheric cold anomalies. The multiple linear regression coefficients are obtained based on MWTS-2 brightness temperatures and the temperatures from the European Centre for Medium-Range Weather Forecasts Reanalysis-5 (ERA5) in the training period of three weeks before the month of targeted typhoons. The proposed MWTS-2 warm-core retrieval can well capture the radial and vertical temporal evolutions of the temperature anomalies of the typhoons Francisco, Lekima, and Krosa. The sizes of the warm-core anomalies of typhoons Lekima and Krosa retrieved by the MWTS-2 are horizontally and vertically similar to and stronger than those of the ERA5. Compared with the ERA5 reanalysis in August 2019, the biases for MWTS-2 temperature retrievals are smaller than ±0.25 K, with root-mean-square errors (RMSEs) smaller than and 2.0 K at all altitudes. Additionally, the location of the 250-hPa maximum temperature anomaly retrieved by the MWTS-2 is closer to the best track than that of the ERA5. A weak warm-core around 200 hPa and a cold-core anomaly in the middle troposphere are also found in the outer rain bands region due to the effect of evaporation of rainfall.

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Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height and amount

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-1231-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 1231-1248 ◽

Cited By ~ 76

Author(s):

B. H. Kahn ◽

M. T. Chahine ◽

G. L. Stephens ◽

G. G. Mace ◽

R. T. Marchand ◽

...

Keyword(s):

Lower Layer ◽

Cloud Amount ◽

Satellite Observation ◽

Retrieval Algorithm ◽

Cloud Type ◽

Atmospheric Infrared Sounder ◽

Cloud Height ◽

Wide Range ◽

Low Cloud ◽

Height Fields

Abstract. The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS) is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat-AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO-AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km) for clouds ≥7 km (<7 km). The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed.

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Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements

Journal of Climate ◽

10.1175/jcli-d-19-0523.1 ◽

2020 ◽

Vol 33 (16) ◽

pp. 6971-6988 ◽

Cited By ~ 1

Author(s):

Simon Whitburn ◽

Lieven Clarisse ◽

Sophie Bauduin ◽

Maya George ◽

Daniel Hurtmans ◽

...

Keyword(s):

Longwave Radiation ◽

Real Data ◽

Far Infrared ◽

Data Retrieval ◽

Detection Algorithm ◽

Retrieval Algorithm ◽

Tropical Region ◽

Cloud Detection ◽

Distribution Models ◽

Spectrally Resolved

AbstractSpace-based measurements of the outgoing longwave radiation (OLR) are essential for the study of Earth’s climate system. While the CERES instrument provides accurate measurements of this quantity, its measurements are not spectrally resolved. Here we present a high-resolution OLR product (sampled at 0.25 cm−1), derived from measurements of the IASI satellite sounder. The applied methodology relies on precalculated angular distribution models (ADMs). These are usually calculated for tens to hundreds of different scene types (characterized by surface and atmosphere parameters). To guarantee accurate results in the range 645–2300 cm−1 covered by IASI, we constructed ADMs for over 140 000 scenes. These were selected from one year of CAMS reanalysis data. A dissimilarity-based selection algorithm was applied to choose scenes as different from each other as possible, thereby maximizing the performance on real data, while keeping the number of scenes manageable. A comparison of the IASI OLR integrated over the 645–2300 cm−1 range was performed with the longwave broadband OLR products from CERES and the AIRS instrument. The latter are systematically higher due to the contribution of the far infrared to the total IR spectral range, but as expected exhibit generally high spatial correlations with the IASI OLR, except for some areas in the tropical region. We also compared the IASI OLR against the spectrally resolved OLR derived from AIRS. A good agreement was found above 1200 cm−1 while AIRS OLR appeared to be systematically higher in the atmospheric window region, likely related to differences in overpass time or to the use of a different cloud detection algorithm.

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Enhanced MOPITT data coverage through cloud detection improvement

10.5194/amt-2021-112 ◽

2021 ◽

Author(s):

Heba S. Marey ◽

James R. Drummond ◽

Dylan B. A. Jones ◽

Helen Worden ◽

Merritt N. Deeter ◽

...

Keyword(s):

Lower Troposphere ◽

Detection Algorithm ◽

Cloud Detection ◽

Detection Scheme ◽

Cloud Height ◽

Standard Product ◽

Low Cloud ◽

Data Coverage ◽

Moderate Resolution Imaging Spectroradiometer ◽

Cloud Mask

Abstract. The Measurements of Pollution in the Troposphere (MOPITT) satellite instrument has been measuring global tropospheric carbon monoxide (CO) since March 2000, providing the longest nearly continuous record of CO from space. During its long mission the data processing algorithms have been updated to improve the quality of CO retrievals and the sensitivity to the lower troposphere. Currently, MOPITT retrievals are only performed for clear-sky observations or over low clouds for ocean scenes. Compared to all observed radiances, successful retrieval rates are about 30 % and 40 % between 90° S–90° N and 60° S–60° N, respectively. Spatial seasonal variations show that while MOPITT data coverage in some places reaches 30 % in summer, this number can drop to less than 10 % in winter due to significantly increased cloud cover. Therefore, we investigate the current MOPITT cloud detection algorithm and consider approaches to increase the data coverage. The MOPITT CO total column (TC) data were modified by turning off the cloud detection scheme to allow a CO retrieval result regardless of their cloud status. Analyses of the standard CO TC product (cloud filtered) and non-standard product (non-cloud masked) were conducted for selected days. Results showed some coherent structures that were observed frequently in the non-masked CO product that were not present in the standard product and could potentially be actual CO features. A corresponding analysis of Moderate Resolution Imaging Spectroradiometer(MODIS) cloud height and cloud mask products along with MOPITT cloud flag descriptors was conducted in order to understand the cloud conditions present for these apparently physical CO features. Results show that a significant number of low cloud CO retrievals were rejected in the standard product. Those missing areas match the coherent patterns that were detected in the non-masked CO product. Many times, these structures were also seen in the Infrared Atmospheric Sounding Interferometer (IASI) CO TC product indicating actual CO plumes. Multi-angle Imaging SpectroRadiometer (MISR) data on the Terra satellite were also employed for cloud height comparison with MODIS. Comparisons of MODIS and MISR cloud height data indicate remarkable agreement which is encouraging for the possibility of incorporating MODIS cloud height in the MOPITT cloud detection scheme. Statistics of the global assessment of the potential use of MODIS cloud height shows that MOPITT data increases significantly when cloud heights less than 2 km in height are incorporated in the retrievals. However quality indices should be defined and produced to ensure sufficient retrieval quality.

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Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height and amount

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-13915-2007 ◽

2007 ◽

Vol 7 (5) ◽

pp. 13915-13958 ◽

Cited By ~ 8

Author(s):

B. H. Kahn ◽

M. T. Chahine ◽

G. L. Stephens ◽

G. G. Mace ◽

R. T. Marchand ◽

...

Keyword(s):

Lower Layer ◽

Cloud Amount ◽

Satellite Observation ◽

Retrieval Algorithm ◽

Cloud Type ◽

Atmospheric Infrared Sounder ◽

Cloud Height ◽

Wide Range ◽

Low Cloud ◽

Height Fields

Abstract. The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS) is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat–AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO–AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km) for clouds ≥7 km (<7 km). The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed.

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Daytime Cloud Detection Algorithm Based on a Multitemporal Dataset for GK-2A Imagery

Remote Sensing ◽

10.3390/rs13163215 ◽

2021 ◽

Vol 13 (16) ◽

pp. 3215

Author(s):

Soobong Lee ◽

Jaewan Choi

Keyword(s):

Vegetation Index ◽

Near Infrared ◽

Normalized Difference Vegetation Index ◽

Infrared Imaging ◽

Satellite Observation ◽

Detection Algorithm ◽

Cloud Detection ◽

Surface Information ◽

Quantitative Results ◽

Filtering Technique

Cloud detection is an essential and important process in remote sensing when surface information is required for various fields. For this reason, we developed a daytime cloud detection algorithm for GEOstationary KOrea Multi-Purpose SATellite 2A (GEO-KOMPSAT-2A, GK-2A) imagery. For each pixel, the filtering technique using angular variance, which denotes the change in top of atmosphere (TOA) reflectance over time, was applied, and filtering technique by using the minimum TOA reflectance was used to remove remaining cloud pixels. Furthermore, near-infrared (NIR) and normalized difference vegetation index (NDVI) images were applied with dynamic thresholds to improve the accuracy of the cloud detection results. The quantitative results showed that the overall accuracy of proposed cloud detection was 0.88 and 0.92 with Visible Infrared Imaging Radiometer Suite (VIIRS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), respectively, and indicated that the proposed algorithm has good performance in detecting clouds.

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The Structure of Low-Altitude Clouds over the Southern Ocean as Seen by CloudSat

Journal of Climate ◽

10.1175/jcli-d-11-00131.1 ◽

2012 ◽

Vol 25 (7) ◽

pp. 2535-2546 ◽

Cited By ~ 37

Author(s):

Yi Huang ◽

Steven T. Siems ◽

Michael J. Manton ◽

Luke B. Hande ◽

John M. Haynes

Keyword(s):

Southern Ocean ◽

Liquid Water ◽

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Lower Boundary ◽

Peak Frequency ◽

Detection Algorithm ◽

Cloud Detection ◽

Low Altitude ◽

Ice Water

Abstract A climatology of the structure of the low-altitude cloud field (tops below 4 km) over the Southern Ocean (40°–65°S) in the vicinity of Australia (100°–160°E) has been constructed with CloudSat products for liquid water and ice water clouds. Averaging over longitude and time, CloudSat produces a roughly uniform cloud field between heights of approximately 750 and 2250 m across the extent of the domain for both winter and summer. This cloud field makes a transition from consisting primarily of liquid water at the lower latitudes to ice water at the higher latitudes. This transition is primarily driven by the gradient in the temperature, which is commonly between 0° and −20°C, rather than by direct physical observation. The uniform lower boundary is a consequence of the CloudSat cloud detection algorithm being unable to reliably separate radar returns because of the bright surface versus returns due to clouds, in the lowest four range bins above the surface. This is potentially very problematic over the Southern Ocean where the depth of the boundary layer has been observed to be as shallow as 500 m. Cloud fields inferred from upper-air soundings at Macquarie Island (54.62°S, 158.85°E) similarly suggest that the peak frequency lies between 260 and 500 m for both summer and winter. No immediate explanation is available for the uniformity of the cloud-top boundary. This lack of a strong seasonal cycle is, perhaps, remarkable given the large seasonal cycles in both the shortwave (SW) radiative forcing experienced and the cloud condensation nuclei (CCN) concentration over the Southern Ocean.

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Rapid Near-Infrared Spectrophotometric Method for Determination of Meprobamate in Meprobamate Tablets

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/51.3.616 ◽

1968 ◽

Vol 51 (3) ◽

pp. 616-618

Author(s):

Stephen Sherken

Keyword(s):

Standard Deviation ◽

Rapid Method ◽

Spectrophotometric Method ◽

Near Infrared ◽

Powder Mixtures ◽

Average Recovery ◽

Near Ir ◽

Good Agreement

Abstract A new rapid method is presented for the analysis of meprobamate in meprobamate tablets, in which the meprobamate is quantitatively dissolved in alcohol-free chloroform and the solution scanned on a spectrophotometer in the near-IR region. The method is rapid and shows good agreement with the official NF XII procedure. Assay of eight commercial samples ranged from 98.5 to 101.6% of labeled amount. Analysis of five authentic meprobamate powder mixtures showed an average recovery of 100.3 ± 0.73%. Collaborative recoveries on two authentic meprobamate powder mixtures averaged 104.0 and 98.7%, respectively. With a standard deviation of ± 2 % some of the collaborators reported that they had difficulty with their instruments in the near-IR region, but not with the method itself. The method was recommended for adoption as official, first action.

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Global cloud top height retrieval using SCIAMACHY limb spectra: model studies and first results

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-8295-2015 ◽

2015 ◽

Vol 8 (8) ◽

pp. 8295-8352 ◽

Cited By ~ 6

Author(s):

K.-U. Eichmann ◽

L. Lelli ◽

C. von Savigny ◽

H. Sembhi ◽

J. P. Burrows

Keyword(s):

Lower Stratosphere ◽

Volcanic Eruptions ◽

Cirrus Clouds ◽

Detection Sensitivity ◽

Retrieval Algorithm ◽

Transfer Model ◽

Cloud Detection ◽

The Tropics ◽

The Impact ◽

Good Agreement

Abstract. Cloud top heights (CTH) were retrieved for the period 1 January 2003 to 7 April 2012 using height-resolved limb spectra measured with the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on board ENVISAT (ENVIronmental SATellite). In this study, we tested the sensitivity of the colour index method used in the retrieval code SCODA (SCIAMACHY Cloud Detection Algorithm) and the accuracy of the retrieved CTHs in comparison to other methods. Sensitivity studies using the radiative transfer model SCIATRAN showed that the method is capable of generally detecting cloud tops down to about 5 km and very thin cirrus clouds even up to the tropopause. Volcanic particles can also be detected that occasionally reach the lower stratosphere. Low clouds at 2–3 km can only be retrieved under very clean atmospheric conditions, as light scattering of aerosols interferes with the cloud retrieval. Upper tropospheric ice clouds are detectable for cloud optical depths down to about τN = 0.005, which is in the subvisual range. The detection sensitivity decreases towards the surface. An optical thickness of roughly 0.1 was the lower detection limit for water cloud top heights at 5 km. This value is much lower than thresholds reported for the passive cloud detection in nadir viewing direction. Comparisons with SCIAMACHY nadir cloud top heights, calculated with the Semi-Analytical CloUd Retrieval Algorithm (SACURA), showed a good agreement in the global cloud field distribution. But only opaque clouds (τN > 5) are detectable with the nadir passive retrieval technique in the UV-visible and infrared wavelength range. So due to the frequent occurrence of thin and sub-visual cirrus clouds in the tropics, large cloud top height deviations were detected between both viewing geometries. Also the land/sea contrast seen in nadir retrievals was not detected in limb mode. Co-located cloud top height measurements of the limb viewing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT for the period from January 2008 to March 2012 were compared, showing good agreement to within 1 km, which is smaller than the vertical field of view of both instruments. Lower stratospheric aerosols from volcanic eruptions occasionally interfered with the cloud retrieval and inhibited detection of tropospheric clouds. Examples of the impact of these events are shown for the volcanoes Kasatochi in August 2008, Sarychev Peak in June 2009, and Nabro in June 2010. Long-lasting aerosol layers were detected after these events in the Northern Hemisphere down to the tropics. Particle top heights up to about 22 km were retrieved in 2009, when the enhanced lower stratospheric aerosol layer persisted for about 7 months. Up to about 82 % of the Northern hemispheric lower stratosphere between 30° and 70° was covered by scattering particles in August 2009 and nearly half in October 2008.

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