Water Absorption Bands Research Articles

HDO and H<sub>2</sub>O total column retrievals from TROPOMI shortwave infrared measurements

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) on board the European Space Agency Sentinel-5 Precursor mission is scheduled for launch in the last quarter of 2016. As part of its operational processing the mission will provide CH4 and CO total columns using backscattered sunlight in the shortwave infrared band (2.3 µm). By adapting the CO retrieval algorithm, we have developed a non-scattering algorithm to retrieve total column HDO and H2O from the same measurements under clear-sky conditions. The isotopologue ratio HDO ∕ H2O is a powerful diagnostic in the efforts to improve our understanding of the hydrological cycle and its role in climate change, as it provides an insight into the source and transport history of water vapour, nature's strongest greenhouse gas. Due to the weak reflectivity over water surfaces, we need to restrict the retrieval to cloud-free scenes over land. We exploit a novel 2-band filter technique, using strong vs. weak water or methane absorption bands, to prefilter scenes with medium-to-high-level clouds, cirrus or aerosol and to significantly reduce processing time. Scenes with cloud top heights ≲1 km, very low fractions of high-level clouds or an aerosol layer above a high surface albedo are not filtered out. We use an ensemble of realistic measurement simulations for various conditions to show the efficiency of the cloud filter and to quantify the performance of the retrieval. The single-measurement precision in terms of δD is better than 15–25 ‰ for even the lowest surface albedo (2–4 ‰ for high albedos), while a small bias remains possible of up to ∼ 20 ‰ due to remaining aerosol or up to ∼ 70 ‰ due to remaining cloud contamination. We also present an analysis of the sensitivity towards prior assumptions, which shows that the retrieval has a small but significant sensitivity to the a priori assumption of the atmospheric trace gas profiles. Averaging multiple measurements over time and space, however, will reduce these errors, due to the quasi-random nature of the profile uncertainties. The sensitivity of the retrieval with respect to instrumental parameters within the expected instrument performance is < 3 ‰, which represents only a small contribution to the overall error budget. Spectroscopic uncertainties of the water lines, however, can have a larger and more systematic impact on the performance of the retrieval and warrant further reassessment of the water line parameters. With TROPOMI's high radiometric sensitivity, wide swath (resulting in daily global coverage) and efficient cloud filtering, in combination with a spatial resolution of 7 × 7 km2, we will greatly increase the amount of useful data on HDO, H2O and their ratio HDO ∕ H2O. We showcase the overall performance of the retrieval algorithm and cloud filter with an accurate simulation of TROPOMI measurements from a single overpass over parts of the USA and Mexico, based on MODIS satellite data and realistic conditions for the surface, atmosphere and chemistry (including isotopologues). This shows that TROPOMI will pave the way for new studies of the hydrological cycle, both globally and locally, on timescales of mere days and weeks instead of seasons and years and will greatly extend the HDO ∕ H2O datasets from the SCIAMACHY and GOSAT missions.

Detection of protein deposits using NIR spectroscopy

ABSTRACTThe aim of this study was to determine if it is possible to distinguish between the groups of spoiled and unspoiled soft contact lenses using near-infrared spectroscopy and new analytical approach – Aquaphotomics. Using the principal component analysis, it was established that the absorbance spectra of worn and new contact lenses are differed at water absorption band related to hydration of proteins. Detection of proteins thus was performed indirectly by using vibrations of water molecules. This exploratory study showed that near-infrared spectroscopy and Aquaphotomics have potential for non-invasive, chemical-free detection of protein deposits on hydrated soft contact lenses.

Remote Sensing of Grass Response to Drought Stress Using Spectroscopic Techniques and Canopy Reflectance Model Inversion

The aim of this study was to follow the response to drought stress in a Poa pratensis canopy exposed to various levels of soil moisture deficit. We tracked the changes in the canopy reflectance (450–2450 nm) and retrieved vegetation properties (Leaf Area Index (LAI), leaf chlorophyll content (Cab), leaf water content (Cw), leaf dry matter content (Cdm) and senescent material (Cs)) during a drought episode. Spectroscopic techniques and radiative transfer model (RTM) inversion were employed to monitor the gradual manifestation of drought effects in a laboratory setting. Plots of 21 cm × 14.5 cm surface area with Poa pratensis plants that formed a closed canopy were divided into a well-watered control group and a group subjected to water stress for 36 days. In a regular weekly schedule, canopy reflectance and destructive measurements of LAI and Cab were taken. Spectral analysis indicated the first sign of stress after 4–5 days from the start of the experiment near the water absorption bands (at 1930 nm, 1440 nm) and in the red (at 675 nm). Spectroscopic techniques revealed plant stress up to 6 days earlier than visual inspection. Of the water stress-related vegetation indices, the response of Normalized Difference Water Index (NDWI_1241) and Normalized Photochemical Reflectance Index (PRI_norm) were significantly stronger in the stressed group than the control. To observe the effects of stress on grass properties during the drought episode, we used the RTMo (RTM of solar and sky radiation) model inversion by means of an iterative optimization approach. The performance of the model inversion was assessed by calculating R2 and the Normalized Root Mean Square Error (RMSE) between retrieved and measured LAI (R2 = 0.87, NRMSE = 0.18) and Cab (R2 = 0.74, NRMSE = 0.15). All parameters retrieved by model inversion co-varied with soil moisture deficit. However, the first strong sign of water stress on the retrieved grass properties was detected as a change of Cw followed by Cab and Cdm in the earlier stages. The results from this study indicate that the spectroscopic techniques and RTMo model inversion have a promising potential of detecting stress on the spectral reflectance and grass properties before they become visibly apparent.

Quantitative and simultaneous non-invasive measurement of skin hydration and sebum levels.

We report a method on quantitative and simultaneous non-contact in-vivo hydration and sebum measurements of the skin using an infrared optical spectroscopic set-up. The method utilizes differential detection with three wavelengths 1720, 1750, and 1770 nm, corresponding to the lipid vibrational bands that lay "in between" the prominent water absorption bands. We have used an emulsifier containing hydro- and lipophilic components to mix water and sebum in various volume fractions which was applied to the skin to mimic different oily-dry skin conditions. We also measured the skin sebum and hydration values on the forehead under natural conditions and its variations to external stimuli. Good agreement was found between our experimental results and reference values measured using conventional biophysical methods such as Corneometer and Sebumeter.

DETECTION OF H 2 O AND EVIDENCE FOR TiO/VO IN AN ULTRA-HOT EXOPLANET ATMOSPHERE

We present a primary transit observation for the ultra hot (Teq~2400K) gas giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range. The 1.4 micron water absorption band is detected at high confidence (5.4 sigma) in the planetary atmosphere. We also reanalyze ground-based photometric lightcurves taken in the B, r', and z' filters. Significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this difference, and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1.12-1.3 micron wavelength range, possibly due to iron hydride absorption. If confirmed, WASP-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs, and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion.

GS0610 エタノール水溶液の拡散係数の温度依存性に関する実験的考察

Temperature dependence of diffusion coefficient of ethanol in dilute ethanol aqueous solutions is investigated by using a simultaneous imaging method of temperature and concentration. The simultaneous imaging is achieved by absorption imaging with two wavelengths of 1905 nm and 1935 nm in the ν_2+ν_3 absorption band of water. The absorbance at 1905 nm is the most sensitive to the temperature in the band but that at 1935 nm is insensitive. Whereas, the absorbances at both wavelength are highly sensitive to the water molar fraction, which is inversely proportional to the ethanol concentration. When a 2 wt% ethanol aqueous solution and pure water flowed in parallel through a microfluidic channel, the concentration changes by diffusion mixing were measured at different temperatures, and the diffusion coefficients were determined by fitting the analytical solution of one-dimensional diffusion equation to the measured concentration data.

Profile and Precipitation Retrievals and Validation Based on Geostationary Sub-Millimeter Atmospheric Sounder

The key factors of temporal and spatial resolution for typhoon observation played an important role in the design of radiometer used for observing typhoon. The NCEP (National Centres for Environmental Prediction) operational global analysis data prepared operationally every six hours were used as the initial field for mesoscale weather research and forecasting model (WRF) and drove the model to output atmospheric parameters such as hydrometeor content, temperature and humidity profiles at different time, which were inputs for the Atmospheric Radiative Transfer Simulator (ARTS) to calculate brightness temperature observed from geostationary earth orbit at oxygen absorption and water absorption band. The atmospheric humidity and temperature profiles of typhoon domain were retrieved from geostationary sub-millimetre atmospheric sounder. The results show that the profile retrievals using BP-NN algorithm have a best agreement with those from radiosonde, which is less than 20% and 1 K of root mean square error, respectively. For precipitation rate retrievals, much better agreement with rain gauge and ECMWF datasets, the RMS is between 0.84 to 32.4 mm/h for sea surface 0.89 and 36.13 mm/h for land surface according to the classification by precipitation type.

Optical properties of tumor tissues grown on the chorioallantoic membrane of chicken eggs: tumor model to assay of tumor response to photodynamic therapy.

Herein, the optical adequacy of a tumor model prepared with tumor cells grown on the chorioallantoic membrane (CAM) of a chicken egg is evaluated as an alternative to the mouse tumor model to assess the optimal irradiation conditions in photodynamic therapy (PDT). The optical properties of CAM and mouse tumor tissues were measured with a double integrating sphere and the inverse Monte Carlo technique in the 350- to 1000-nm wavelength range. The hemoglobin and water absorption bands observed in the CAM tumor tissue (10 eggs and 10 tumors) are equal to that of the mouse tumor tissue (8 animals and 8 tumors). The optical intersubject variability of the CAM tumor tissues meets or exceeds that of the mouse tumor tissues, and the reduced scattering coefficient spectra of CAM tumor tissues can be equated with those of mouse tumor tissues. These results confirm that the CAM tumor model is a viable alternative to the mouse tumor model, especially for deriving optimal irradiation conditions in PDT.

Bulk Optical Properties of Potato Flesh in the 500–1900 nm Range

In this study, the optical properties of potato flesh tissue were estimated using double-integrating sphere (DIS) measurements combined with an inverse adding-doubling (IAD) light propagation model. Total reflectance, total transmittance, and unscattered transmittance were measured for the wavelength range 500–1900 nm with 5-nm resolution. From these measurements, the bulk optical properties (absorption coefficient, scattering coefficient, and anisotropy factor) of 53 potato tubers of the Hermes cultivar were estimated. The estimated absorption coefficient spectra were dominated by water and starch absorption bands, the main chemical components of potato tissue. Comparison of these values to those reported in literature for similar products showed comparable absorption profiles. The obtained scattering coefficient spectra showed a smooth decrease from 166 to 160 cm−1 in the near-infrared (NIR) spectral range with increasing wavelength, which is common for biological tissues. The anisotropy factor spectra obtained for the full wavelength range studied ranged between 0.949 and 0.959 with a maximum variability of 0.009 among the set of samples used. The information obtained in this study is essential to understand the effects of absorption and scattering on the propagation of light through the potato tubers in order to design more efficient sensors for non-destructive quality evaluation.

Surface-selective laser sintering of thermolabile polymer particles using water as heating sensitizer

We report the implementation of a novel scheme for surface-selective laser sintering (SSLS) of polymer particles, based on using water as a sensitizer of laser heating and sintering of particles as well as laser radiation at a wavelength of , corresponding to the strong absorption band of water. A method of sintering powders of poly(lactide-co-glycolide), a hydrophobic bioresorbable polymer, after modifying its surface with an aqueous solution of hyaluronic acid is developed. The sintering thresholds for wetted polymer are by lower than those for sintering in air. The presence of water restricts the temperature of the heated polymer, preventing its thermal destruction. Polymer matrices with a developed porous structure are obtained. The proposed SSLS method can be applied to produce bioresorbable polymer matrices for tissue engineering.

A method for distinguishing between liquid samples by calculation of the initial moments using their infrared spectra

In this paper, a method for distinguishing between liquid samples that are sensitive to the influence of low-intensity physicochemical factors is described. It is based on the calculation of the initial moments of the intensity distribution series in their infrared spectra and comparison of the obtained values with each other. Reliable signs of the coincidence of liquid samples that were obtained in the experiment were used to distinguish distilled water at–0.5 ± 0.5 and–3.0 ± 0.5±C, and at–3.0 ± 0.5 and–5.0 ± 0.5°C, and to distinguish between distilled and tap water at 25.0 ± 0.5°C. For each sample, the moments were calculated for the bending (1640 cm–1), combination (2090 cm–1), and stretching (3370 cm–1) water absorption bands. It was found that when comparing distilled water at–0.5 ± 0.5 and–3.0 ± 0.5°C the greatest differences are observed for the bending band (50%). When considering distilled water at–3.0 ± 0.5 and–5.0 ± 0.5°C, the greatest differences occur for the stretching band (54%). When comparing distilled water at 25.0 ± 0.5°C and tap water at 25.0 ± 0.5°C, the greatest differences were observed for the bending band (86%).

Relationship between surface soil water content, evaporation rate, and water absorption band depths in SWIR reflectance spectra

Abstract The spectral reflectance of three soil samples – selected to represent a range of particle size distribution, texture, and drying characteristics – was monitored as the samples progressed from fully saturated to air dry. Band depths of prominent water absorption features in the near and shortwave infrared, centered at 970 nm, 1160 nm, 1440 nm, and 1930 nm, were then compared to the surface water content, with the expectation that this metric would be characteristic of the soil moisture content and be largely independent of soil properties. As expected, the band depths at 970 nm and 1160 nm decreased monotonically as the water content decreased. Unfortunately, these bands were only detectable in the sample consisting of large, reflective particles and large pore spaces (quartz sand). That they were not apparent in the darker soils with smaller particles and pore spaces suggests that these water absorption bands will not be generally useful for observing surface soil moisture. In contrast, the band depths of the 1440 nm and 1930 nm absorption features were very responsive to the water content over the entire drying cycle, providing a strong, but more complex signal, with the band depth initially increasing with decreasing water content before reaching a maximum and finally decreasing late in the drying cycle. The change in band depth at 1930 nm was particularly interesting since it reached a maximum coincident with the transition from constant evaporation rate (stage-1 drying) to a much slower evaporation rate (stage-2 drying) for all three soils. A simple mathematical model suggests that the pattern of change in the band depth is related to the near extinction of light at the band center relative to the band shoulders, which can be related to a specific water optical path length. The maximum absorption band depth at 1930 nm (and the associated water optical path length) appears to coincide with a trace amount of water present in the pore spaces for all three soil samples, which is consistent with the transition in drying rates.

CHARACTERIZING THE ATMOSPHERES OF THE HR8799 PLANETS WITH HST /WFC3

We present results from a Hubble Space Telescope (HST) program characterizing the atmospheres of the outer two planets, in the HR8799 system. The images were taken over 15 orbits in three near-infrared medium-band filters - F098M, F127M and F139M - using the Wide Field Camera 3. One of the three filters is sensitive to water absorption band inaccessible from ground-based observations, providing a unique probe of the thermal emission from the atmospheres of these young giant planets. The observations were taken at 30 different spacecraft rolls to enable angular differential imaging, and the full data set was analyzed with the Karhunen-Loeve Image Projection (KLIP) routine, an advanced image processing algorithm adapted to work with HST data. To achieve the required high contrast at sub arcsecond resolution, we utilized the pointing accuracy of HST in combination with an improved pipeline designed to combine the dithered, angular differential imaging data with an algorithm designed to both improve the image resolution and accurately measure the photometry. The results include F127M ($J$) detections of the outer planets, HR8799 b and c and the first detection of HR8799 b in the water-band (F139M) filter. The F127M photometry for HR8799 c agrees well with fitted atmospheric models resolving a long standing difficulty to model the near-IR flux for the planet consistently

Quantitative phase analysis of lateritic bauxite with NIR-spectroscopy

The applicability of near-infrared (NIR) spectroscopy as tool for continuous and direct quality control of bauxite material on conveyor belts at mining sites was assessed. Modal quantifications of the bauxite mineralogy were performed by X-ray powder diffractions (XRPD)/Rietveld-analysis on 200 aliquots derived from 4 charges from the same sample locality and compared to Near Infrared (NIR) spectra measured in reflectance mode. Based on the two methods multivariate calibration models from partial least squares (PLS) regressions were evolved. Laboratory scaled results show a predictability of the major mineralogical phases (gibbsite and kaolinite) within 2.5wt% (1σ).In order to test the quality of the laboratory scaled calibrations and their applicability to mining procedures, additional measurements were performed using an industrial NIR-analyzer from ABB that was specifically developed for conveyor belts. Results show that for an industrial usage two crucial points have to be considered: (1) The modal mineralogy of individual chunks of material depends on the grain size. Specifically, larger chunks contain a higher modal content of gibbsite and often are coated by a kaolinite-rich shell. Therefore, modal mineralogy determined by NIR spectroscopy in reflectance mode is biased by the grain size. In order to yield unbiased measurements, the material must be crushed at least to cm-size. (2) Humidity has strong influence on the NIR-spectra by changing band intensities. Therefore, in order to get accurate predictions, absorption bands of water have to be taken into account as additional constituent in the calibration models.

Modeling Shallow Groundwater Depth Using Hyperion Hyperspectral Imagery

Current study was conducted in order to finding the best models to estimating groundwater depth using Hyperion hyperspectral satellite imagery in the sugarcane fields located in the southwest of Iran. For this purpose ground water level was measured in 132 observation wells from the beginning of May 2010 till end of September 2010, twice per week, in the Hakim Farabi farming and industrial lands. Moreover, from the other collected information like daily weather information, age and variety of sugarcane, planting and harvesting date of plants, managerial operations such as date and amount of the fertilization, irrigation and drainage information in the Hakim Farabi farming and industrial lands were used. In a same time with measuring the ground data, a hyperspectral satellite image of Hyperion sensor was acquired on September 2, 2010. After applying necessary pre-processing on the image, the changes in the spectral reflectance of the sugarcane under different values of groundwater depths was studied. Afterwards, it was tried to obtain appropriate models for estimating ground water depth. For this purpose, capability of 21 vegetation indices ,related to defferent regions of spectral reflectance of crops, was studied. Besides of these indices three new vegetation indices (SWSI-1, SWSI-2 and SWSI-3) were developed in this study. Results show that, variations of groundwater depths have a significant effect on spectral reflectance of sugarcane. Among the vegetation indices, indices related to water absorption bands or based on a combination of chlorophyll and water absorption bands had the highest correlation with groundwater depth. Obtained models from the two vegetation indices developed in this study (SWSI-1, SWSI-3) and NDWI yield the best results for estimating groundwater depth with R2 of 0.48, 0.48 and 0.47 and root mean square errors of 8.20, 8.25 and 7.98 cm respectively. Conclusions from this study indicate that using hyperspectral satellite imagery to monitoring water table in the sugarcane fields has an acceptable, fast and economical results.

The use of infrared self-emission measurements to retrieve surface temperature of levitating water droplets

Levitating small water droplets formed from the upward flow of steam and entrained air above the heated water surface are studied. The case of relatively large droplets in the middle of a droplet cluster which is practically immobile at a small distance from the water surface is considered. The close-up infrared measurements in the spectral absorption band of water are used to identify temperature of the upper surface of the droplet. Both the directional spectral emittance of water surface and the spectral sensitivity of the device are taken into account to formulate an inverse problem for the integral equation. The numerical solution of this problem showed that temperature is minimal at the top of droplet and increases sharply towards the droplet equator. This temperature difference increases almost linearly with the droplet size. The results obtained are expected to be useful for more detailed physical analysis and possible modeling of complex behavior of the levitating droplet clusters.

CLOUD STRUCTURE OF THE NEAREST BROWN DWARFS: SPECTROSCOPIC VARIABILITY OF LUHMAN 16AB FROM THEHUBBLE SPACE TELESCOPE

The binary brown dwarf WISE J104915.57$-$531906.1 (also Luhman 16AB), composed of a late L and early T dwarf, is a prototypical L/T transition flux reversal binary located at only 2 pc distance. Luhman 16B is a known variable whose light curves evolve rapidly. We present spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 h using HST/WFC3 at 1.1 to 1.66 $\mu$m. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above $\approx$0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f_sed=2, Teff=1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 $\mu$m, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very similar to the other two known highly variable early T dwarfs. A two-component cloud model accounts for most of the variability, although small deviations are seen in the water absorption band. We fit the mean spectrum and relative amplitudes with a linear combination of two models of a warm, thinner cloud (Teff=1300 K, fsed=3) and a cooler, thicker cloud (Teff=1000-1100 K, f_sed=1), assuming out-of-equilibrium atmospheric chemistry. A cloud as for Luhman 16A but with holes cannot reproduce the variability of Luhman 16B, indicating more complex cloud evolution through the L/T transition. The projected separation of the binary has decreased by $\approx$0.3'' in 8 months.

Design of an ultrashort optical transmission cell for vacuum ultraviolet spectroscopy of supercritical fluids.

We present the design and characteristics of an ultrathin flow cell optimized for vacuum ultraviolet transmission spectroscopy experiments on supercritical fluids. The cell operates satisfactorily at pressures up to 300 bar and temperatures up to 390 °C. The variable path length concept of the cell allows for optical transmission studies of analytes ranging from dense condensed-phase systems to gas-phase systems. The path length of the cell can be adjusted from hundreds of nanometers to hundreds of micrometers by an exchange of a variable thickness spacer sandwiched between two sapphire windows. In the path length range from nanometers to single micrometers, metal vapor deposited on one or both of the two sandwiched optical windows constitute the spacer. Spacers with thicknesses of 2 μm and greater can be constructed from simple commercially available metal foils. The cell has been used to measure the lowest-lying absorption band of water in both the vapor and condensed phases from room temperature up to and above the critical point. It has also found application in the studies of aqueous ions and nonaqueous liquids including various common organic solvents and carbon dioxide.

First-Order Phase Transition in Liquid Water in Terms of the Mode Structure of Absorption Spectrum in the Near-IR Range

Absorption spectra of liquid water H2O are investigated in the region 4500–5600 cm–1 at temperatures from –53.0 to +20.3°C. The absorption band is decomposed into component modes at (I) 4700, (II) 4890, (III) 5080, and (IV) 5200 cm–1 whose centers are shifted slightly with temperature. Modes (II), (III), and (IV) are present in the spectrum of liquid water, whereas modes (I), (II), and (III) are registered in the spectrum of ice. The appearance of the ordered crystalline lattice is characterized by the occurrence of low-frequency mode (I) and by the disappearance of high-frequency component (IV) of the water absorption band in the region 4500–5600 cm–1. The spectral regions and temperature ranges in which the structure is changed during phase transition are determined.

HST ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS

We present time-resolved near-infrared spectroscopy of two L5 dwarfs, 2MASS J18212815+1414010 and 2MASS J15074759-1627386, observed with the Wide Field Camera 3 instrument on the Hubble Space Telescope (HST). We study the wavelength dependence of rotation-modulated flux variations between 1.1 $\mu$m and 1.7 $\mu$m. We find that the water absorption bands of the two L5 dwarfs at 1.15 $\mu$m and 1.4 $\mu$m vary at similar amplitudes as the adjacent continuum. This differs from the results of previous HST observations of L/T transition dwarfs, in which the water absorption at 1.4 $\mu$m displays variations of about half of the amplitude at other wavelengths. We find that the relative amplitude of flux variability out of the water band with respect to that in the water band shows a increasing trend from the L5 dwarfs toward the early T dwarfs. We utilize the models of Saumon & Marley (2008) and find that the observed variability of the L5 dwarfs can be explained by the presence of spatially varying high-altitude haze layers above the condensate clouds. Therefore, our observations show that the heterogeneity of haze layers - the driver of the variability - must be located at very low pressures, where even the water opacity is negligible. In the near future, the rotational spectral mapping technique could be utilized for other atomic and molecular species to probe different pressure levels in the atmospheres of brown dwarfs and exoplanets and uncover both horizontal and vertical cloud structures.