A simple method to relate microwave radiances to upper tropospheric humidity

Buehler, Stefan; John, Viju O.

doi:10.1029/2004jd005111

Cited by 74 publications

(110 citation statements)

References 30 publications

(59 reference statements)

Supporting

Mentioning

106

Contrasting

Order By: Relevance

“…Figure 13 shows brightness temperature histograms for the 183 ± 1 GHz channel on SSMIS, which is sensitive to upper tropospheric moisture (e.g. Buehler and John, 2005) and to deep convection (e.g. Hong et al, 2005).…”

Section: Results Over Landmentioning

confidence: 99%

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

2014

View full text Add to dashboard Cite

Abstract. To simulate passive microwave radiances in allsky conditions requires better knowledge of the scattering properties of frozen hydrometeors. Typically, snow particles are represented as spheres and their scattering properties are calculated using Mie theory, but this is unrealistic and, particularly in deep-convective areas, it produces too much scattering in mid-frequencies (e.g. 30-50 GHz) and too little scattering at high frequencies (e.g. 150-183 GHz). These problems make it hard to assimilate microwave observations in numerical weather prediction (NWP) models, particularly in situations where scattering effects are most important, such as over land surfaces or in moisture sounding channels. Using the discrete dipole approximation to compute scattering properties, more accurate results can be generated by modelling frozen particles as ice rosettes or simplified snowflakes, though hexagonal plates and columns often give worse results than Mie spheres. To objectively decide on the best particle shape (and size distribution) this study uses global forecast departures from an NWP system (e.g. observation minus forecast differences) to indicate the quality of agreement between model and observations. It is easy to improve results in one situation but worsen them in others, so a rigorous method is needed: four different statistics are checked; these statistics are required to stay the same or improve in all channels between 10 GHz and 183 GHz and in all weather situations globally. The optimal choice of snow particle shape and size distribution is better across all frequencies and all weather conditions, giving confidence in its physical realism. Compared to the Mie sphere, most of the systematic error is removed and departure statistics are improved by 10 to 60 %. However, this improvement is achieved with a simple "one-size-fits-all" shape for snow; there is little additional benefit in choosing the particle shape according to the precipitation type. These developments have improved the accuracy of scattering radiative transfer sufficiently that microwave all-sky assimilation is being extended to land surfaces, to higher frequencies and to sounding channels.

show abstract

Section: Results Over Landmentioning

confidence: 99%

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

2014

View full text Add to dashboard Cite

show abstract

“…We average the CPR IWP over the MHS pixel, and select a subset of collocations. For the collocations, only measurements that are within 20 degrees of the equator are used, in order to prevent a signal from the surface (Buehler and John, 2005). Only collocations where the MHS measurement is within 5 degrees of nadir are used, so that no significant limb effect occurs.…”

Section: Comparison Of Bt-iwp Relationsmentioning

confidence: 99%

“…The subset is restricted to pixels over ocean within 20 degrees of the equator, because a warm (and humid) atmosphere prevents the MHS from getting a signal from the surface (Buehler and John, 2005). Due to these restrictions, the neural network is only applicable to the tropics.…”

Section: Developing a Retrieval Using Neural Netsmentioning

confidence: 99%

Collocating satellite-based radar and radiometer measurements – methodology and usage examples

et al. 2010

Self Cite

View full text Add to dashboard Cite

Abstract. Collocations between two satellite sensors are occasions where both sensors observe the same place at roughly the same time. We study collocations between the Microwave Humidity Sounder (MHS) on-board NOAA-18 and the Cloud Profiling Radar (CPR) on-board CloudSat. First, a simple method is presented to obtain those collocations and this method is compared with a more complicated approach found in literature. We present the statistical properties of the collocations, with particular attention to the effects of the differences in footprint size. For 2007, we find approximately two and a half million MHS measurements with CPR pixels close to their centrepoints. Most of those collocations contain at least ten CloudSat pixels and image relatively homogeneous scenes. In the second part, we present three possible applications for the collocations. Firstly, we use the collocations to validate an operational Ice Water Path (IWP) product from MHS measurements, produced by the National Environment Satellite, Data and Information System (NESDIS) in the Microwave Surface and Precipitation Products System (MSPPS). IWP values from the CloudSat CPR are found to be significantly larger than those from the MSPPS. Secondly, we compare the relation between IWP and MHS channel 5 (190.311 GHz) brightness temperature for two datasets: the collocated dataset, and an artificial dataset. We find a larger variability in the collocated dataset. Finally, we use the collocations to train an Artificial Neural Network and describe how we can use it to develop a new MHS-based IWP product. We also study the effect of adding measurements from the High Resolution Infrared Radiation Sounder (HIRS), channels 8 (11.11 µm) and 11 (8.33 µm). This shows a small improvement in the retrieval quality. The collocations described in the article are available for public use.

show abstract

“…The UTH retrieval method of Buehler and John (2005) was confirmed to be well suited for deriving a UTH climatology from AMSU-B Ch18 data. Also, some new light was shed on the known limitations of this method.…”

Section: Discussionmentioning

confidence: 90%

“…These channels have center frequencies of 183.31±1.00, 183.31±3.00, and 183.31±7.00 GHz and will be referred to as Ch18, Ch19, and Ch20, respectively. Recently, Buehler and John (2005) demonstrated that UTH can be derived from AMSU-B Ch18 brightness temperatures with a precision of 2% RH at low UTH values and 7% RH at high UTH values. The same retrieval algorithm was used for the work described here.…”

mentioning

confidence: 99%

A cloud filtering method for microwave upper tropospheric humidity measurements

et al. 2007

Self Cite

View full text Add to dashboard Cite

Abstract. The paper presents a cloud filtering method for upper tropospheric humidity (UTH) measurements at 183.31±1.00 GHz. The method uses two criteria: a viewing angle dependent threshold on the brightness temperature at 183.31±1.00 GHz, and a threshold on the brightness temperature difference between another channel and 183.31±1.00 GHz. Two different alternatives, using 183.31±3.00 GHz or 183.31±7.00 GHz as the other channel, are studied. The robustness of this cloud filtering method is demonstrated by a mid-latitudes winter case study. The paper then studies different biases on UTH climatologies. Clouds are associated with high humidity, therefore the possible dry bias introduced by cloud filtering is discussed and compared to the wet biases introduced by the clouds radiative effect if no filtering is done. This is done by means of a case study, and by means of a stochastic cloud database with representative statistics for midlatitude conditions. Both studied filter alternatives perform nearly equally well, but the alternative using 183.31±3.00 GHz as other channel is preferable, because that channel is less likely to see the Earth's surface than the one at 183.31±7.00 GHz. The consistent result of all case studies and for both filter alternatives is that both cloud wet bias and cloud filtering dry bias are modest for microwave data. The recommended strategy is to use the cloud filtered data as an estimate for the true all-sky UTH value, but retain the unfiltered data to have an estimate of the cloud induced uncertainty. The focus of the paper is on midlatitude data, since atmospheric data to test the filter for that case were readily available. The filter is expected to be applicable also to subtropical and tropical data, but should be further validated with case studies similar to the one presented here for those cases.

show abstract

A simple method to relate microwave radiances to upper tropospheric humidity

Cited by 74 publications

References 30 publications

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

Collocating satellite-based radar and radiometer measurements – methodology and usage examples

A cloud filtering method for microwave upper tropospheric humidity measurements

Contact Info

Product

Resources

About