Measurements/Assumptions to Validate

The quid pro quo (QPQ) measurements in collaboration with existing sites and other activities (e.g. field programs) are an important part of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) validation program. These sites and field programs will provide data relevant to CALIPSO validation at times when the ground-track of the CALIPSO satellite is within a specified coincident distance. Exchange of data between CALIPSO and these sites will occur with no risk and cost to the project and follow appropriate protocols of exchange. Coordination of the validation measurements will be made through the CALIPSO homepage (http://www-calipso.larc.nasa.gov), the QPQ validation website (http://calipsovalidation.hamptonu.edu), email notices, fax, phone, and conventional mail announcements. This document will describe only permanent sites and not field campaigns sponsored and funded by other groups, although these will be pursued.

Sites are invited to collaborate in the QPQ validation program if data produced at these sites validate CALIPSO Level II data products. The number of coincident measurements, measurement and calibration history of the instruments, publications, and location of data files will be gathered or calculated and stored in a database allowing a user to determine the quality of the measurements and easily find what data are available. A web interface will allow the user to search this database to find data based on their own search criteria.

2. Strategy

2.1 Approach

To a considerable degree, data products from the CALIPSO satellite mission will be validated through comparisons with correlative in-situ and remote sensing measurements. For the CALIPSO mission, validation is defined as an assessment of the accuracy and precision of the derived science products by independent means. Assessment of the relative agreement between data sets can occur either through a direct comparison of two or more measurements or, through a comparison of probability distribution functions (PDFs). Direct comparison implies that the correlative measurements view the same atmospheric features (e.g., same cloud or aerosol layers) as observed by all instruments. In the best of circumstances, the instruments would share the same field of view and occur simultaneously. For ground-based systems, matching measurements with satellite observations can be exceedingly difficult because of the brief window of opportunity during a satellite overpass, and especially for spaceborne lidars or radars, with a very narrow field of view. The difference between two measurements that are not collocated in space or time or have different resolutions will include some measure of geophysical variability, which is unrelated to measurement uncertainty. Fortunately, aerosol air masses can have correlation scales of 50-100 km and several hours or more. For clouds, the length scales can be significantly smaller (a few kilometers to tens of kilometers) and lifetimes as short as a few minutes. These length and time scales, thus, provide guidelines on matching requirements needed between sensor systems for aerosol and cloud features. Trajectory analysis may also be employed to improve matching conditions for observations that have large spatial and temporal separations.

An alternative approach to direct comparisons is to consider an ensemble of observations collected over a long period or a variety of conditions. This approach is especially appealing for geophysical phenomena that have very restrictive matching requirements such as for cumulus clouds.

2.2 Data products

Table 1 lists the primary Level 2 data products that will be produced by the CALIPSO satellite mission. Details on these products are provided in the Lidar and Infrared Imaging Radiometer Algorithm Theoretical Basis Documents (ATBDs). The table also provides information on the expected uncertainty and the horizontal and vertical resolution of the products. Correlative measurements of comparable or superior accuracy and resolution should be acquired to validate these CALIPSO data products.

Table 1: CALIPSO Level 2 Aerosol and Cloud Measurements

Data Product	Measurement Capabilities and Uncertainties	Data Product Resolution
Data Product	Measurement Capabilities and Uncertainties	Horizontal	Vertical
Aerosols
Height, thickness	For layers with b > 2.5 x 10^-4km^-1 sr^-1	5km	60 m
Optical depth, t	40% *	5 km	N/A
Backscatter, b_a(z)	20 - 30%	40 km 40 km	Z < 20 km 120 m Z ³ 20 km: 360 m
Extinction, s_a(z)	40 % *	40 km 40 km	z < 20 km 120 m z ³ 20 km: 360 m
Clouds
Height	For layers with b > 1 x 10^-3km^-1 sr^-1	1/3, 1, 5 km	30, 60 m
Thickness	for layers with t < 5	1/3, 1, 5 km	30, 60 m
Optical depth, t	within a factor of 2 for t < 5	5 km	N/A
Backscatter, b_c(z)	20 - 30%	5 km	60 m
Extinction, s_c(z)	within a factor of 2 for t < 5	5 km	60 m
Ice/water phase	Layer by layer	5 km	60 m
Effective emissivity, e	±0.03	1 km	N/A
Ice particle size	±50% for e > 0.2	1 km	N/A
Note: * assumes 30% uncertainty in the aerosol extinction-to-backscatter lidar ratio, S_a

2.3 Aerosols

Clouds and aerosols vary on different spatial and temporal scales and, thus, require different validation strategies. Aerosols typically have longer spatial correlation distances than clouds providing a greater opportunity for coincident comparisons between instruments. An exception to this rule is polar stratospheric clouds (PSCs), which, in most cases, have coincident distances much larger than tropospheric clouds and aerosols.

Aerosol height and thickness will be calculated from the attenuated aerosol backscatter coefficient. Comparisons are needed with similar or superior detection and ranging capabilities such as ground-based lidars or backscattersondes. Because aerosol height and thickness tends to remain fairly consistent over long distances, except near local sources (e. g. smoke stacks, fires, etc.), the coincident distances (50-100 km) between the CALIPSO ground track and validation site can be much larger than for clouds.

For CALIPSO, Level 2 aerosol optical depth and extinction products are retrieved from backscatter measurements. These parameters require validation of the data products and the assumptions used to calculate them; namely, the value of the extinction-to-backscatter ratio, S_a. A layer averaged S_a can be estimated by CALIPSO measurements and a density profile for elevated aerosol layers, but S_a is estimated using a variety of ancillary data for non-elevated layers. A large number of observations in the literature indicate that optical depth and extinction are much more variable than the aerosol layer properties of height and thickness and, therefore, require more stringent coincidence criteria (<50 km).

A high spectral resolution lidar, elevation-scanned backscatter lidar, or 532 nm Raman lidar would be extremely valuable for validating the extinction profile and selection of S_a in the retrieval algorithm. Unfortunately, few of these systems exist worldwide and fewer yet can resolve the boundary layer. A 355 nm Raman lidar would be helpful to validate the extinction profile at 532 and 1064 nm, but the extinction profile would need to be transferred from 355 nm. A backscatter lidar colocated with a sunphotometer would also be suitable to validate the extinction profile and S_a, though assumptions still need to be made to calculate these parameters and the layers would need to have a near-constant lidar ratio. A sunphotometer or multi-filter rotating spectroradiometer (MFRSR) would be useful to validate aerosol optical depth.

2.4 Clouds

Optical properties of clouds are usually more variable horizontally than layers of aerosols. Hogan and Illingworth (2000) find that for cirrus clouds, (the best case) matching errors by stations separated by 5 km were approximately 100% and for 1-2 km the matching error is 25-50%. Therefore, validation of cloud properties will largely rely on statistical techniques. Because correlation scales are small for cloud properties, particularly optical depth, sites with frequent long-term measurements that have many coincident measurements within a short distance will be given high priority.

Cloud height and thickness is calculated in the same manner as for aerosol height and thickness and, therefore, requires such instruments as lidars or backscattersondes. Millimeter cloud radars will also be useful; but, because of the large difference in the detection sensitivities between lidars and radars, data from these instruments will be used in a more limited role for validation. The effect of multiple scattering on the determination of cirrus cloud height and thickness is expected to be small for the limited field of view of CALIPSO so that only attenuated backscatter is necessary to measure cloud height and thickness. These two parameters have the longest horizontal correlation scales for clouds (20-50 km) so that some direct comparisons may be made, particularly for non-convective clouds. Low clouds will be much more difficult to validate from the ground because for most low clouds the returned lidar signal for CALIPSO will be fully attenuated, so that it only cloud top is measured, while a ground lidar will be fully attenuated before reaching cloud top and measure only cloud base. A millimeter wavelength cloud radar may be more useful for these clouds. For nonattenuating low clouds, the effects of multiple scattering will be larger for the CALIPSO lidar and must be considered for all cloud data products.

Cloud optical depth, extinction profiles, and S_c are calculated similar to the analogous aerosol properties, but the correlation scales for clouds are quite small (< 5 km). Surface lidar sites can only be used where the clouds are overcast and uniform on scales similar to the distance between the surface site and the CALIPSO ground track. Only Raman and HSRL lidars can be used to validate cloud optical depth and extinction profiles, while for S_c a 532 or 1064 nm lidar must be present (a 355 nm Raman lidar alone will not suffice). Therefore, surface sites will play a small role in validating these cloud parameters.

Cloud ice/water phase is determined from the 532 nm depolarization ratio. Surface depolarization lidar at 532 nm is best, but a 355 nm depolarization lidar can be helpful, particularly for large particles (> 1 mm), where depolarization changes little with wavelength (Mishchenko et al., 1996). Correlation distances for cloud ice/water phase are larger than other cloud properties and the coincident distance (~ 50 km) may be large enough for direct comparisons.

2.5 IIR derived data products

Comparisons between the CALIPSO IIR and ground-based instruments are needed to support IIR calibration analysis and validation of its derived data products. Correlative measurements are needed along the satellite track that provide knowledge on the degree of cloudiness and altitude of cloud layers, profile information on temperature and humidity, and characterization of surface conditions such as temperature and emissivity. These measurements are needed for day and night satellite overpasses as well as over land and ocean with varying surface conditions.

To illustrate these requirements one can examine the IIR data product for effective emissivity, e_c, of a cloud. This parameter is calculated from the relationship, e_c = (L_i - L_o)/(L_b - L_o), where L_i is the upward radiance measured by the IIR, L_o is the radiance measured in a cloud free atmosphere, and L_b is the radiance from an opaque cloud at the same temperature. This latter term is obtained from temperature and humidity profiles for the cloud height determined from lidar observation. Comparisons with facilities that can independently reproduce this calculation and verify it with surface radiometers will be extremely valuable for evaluating the IIR emissivity product quality.

Cloud particle size is another data product that will be produced from the IIR. It is a challenging product to validate because it may vary considerably over short horizontal distances (< 1 km) and within thin vertical layers (< 300 m). Some sites, notably ARM sites, use a radar-IR or radar-lidar technique to produce particle size measurements. This technique would need to be validated by in-situ measurements of particle sizes before it may be used to directly validate CALIPSO particle size measurements. Effective emissivity and particle size will only be retrieved for thin cirrus and therefore validation will only focus on thin cirrus.

3. Existing Instrument Networks and Individual Sites

The following instrument networks and individual sites have been identified by the CALIPSO validation implementation team as being suitable for participating in validation activities and have been contacted for, or expressed interest in, participating in the QPQ validation program. Each network has a long history of measurements and a measurement and calibration protocol. For each network, a brief description of the network is given followed by a list of pertinent measurements and CALIPSO level II parameters that they validate.

3.1 Aeronet

http://aeronet.gsfc.nasa.gov/

Aeronet is a federation of ground-based remote sensing aerosol networks, largely sunphotometers, around the world. Aerosol optical thickness at 1020, 870, 670, 500, 440, 380, and 240 nm are derived at most places. Sky radiance measurements along the solar alumcantar (i.e. at constant elevation angle with varied azimuth angles) and the solar principal plane (i.e. at constant azimuth angle with varied scattering angles) are made at 440, 670, 870, and 1020 nm to retrieve size distribution and phase function. Aerosol optical thickness is derived every 15 minutes or 0.25 air masses; whichever is more frequent, from an air mass of 7 in the morning to an air mass of 7 in the evening. Each measurement consists of a triplet of measurements at each wavelength that are analyzed for cloud screening and averaged. Sky radiance measurements are taken 6 times a day along the solar alumcantar and 9 times a day along the solar principal plane. Sun photometers are calibrated by the Langley method every 2-3 months, which is then transferred to field sunphotometers pre- and post-deployment to an accuracy of 1-2% for aerosol optical thickness, and every 9-12 months to get an accuracy of 5% for sky radiance.

The following measurements from the Aeronet sites listed in Section 7.1 would be suitable for CALIPSO validation (validated parameters in parentheses):

Sunphotometer (t_a (532 nm), t_a(1064 nm))

3.2 Asian Dust NETwork (AD-Net)

http://info.nies.go.jp:8094/kosapub/index.html

The AD-Net is an international virtual community, which was formed in February 2001. It was setup to provide rapid communication via the Internet on Asian dust events. The network observation of Asian dust was originally started in 1997 mainly with lidar groups in Japan. Since 1998, exchange of Asian dust information with lidar and other surface observations expanded to the East Asia countries of China and Korea. The AD-Net primary observation campaign take place every year in northern springtime from March 1 to May 31. Many of the lidars in the network belong to research programs on the atmospheric radiation and/or regional air-pollution, and the lidars are operated continuously throughout year.

Table 2 presents a list of instruments, the resolution in time and space of available lidar, and the CALIPSO Level II parameters validated for each site in the network.

Table 2: List of instruments, vertical range and resolution, time resolution, and parameters validated for each station within the AD-Net.

Station	Instrument	Lidar range (resolution)	Lidar time resolution	Validated parameter
Beijing	532 nm w/polarization, 1064 nm lidar.	0.1-15 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Cheju	See MPLNET
Chung-Li	532 nm, 1064 m w/polarization lidar	1- 30 km (24 m)		aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Fukue	532 nm w/polarization, 1064 nm lidar.	0.1-15 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Fukuyama	532 nm w/polarization lidar.	0-15 km	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Gwangju	355 nm, 532nm w/polarization, 1064 nm, 387 nm Raman lidar	0.5-30 km (7.5 m)	10 mins.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), t_c(532), s_c(532), t_c(1064), s_c(1064), S_a (532), S_a (1064), S_c(532), S_c(1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Hedo	532 nm w/polarization, 1064 nm lidar.	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Hefei	532 nm w/polarization, 1064 nm lidar.	0-18 km (30 m)	Day and night operation, 15 minute resolution	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Hohhot	532 nm w/polarization lidar	0.1-15 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Miyako-jima	532 w/polarization, 1064 nm lidars	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Nagasaki	532 nm w/polarization, 1064 nm lidar	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Nagoya	355, 532 w/polarization, 1064 nm, and Raman lidar	troposphere and stratosphere (30 m)	5 mins.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), t_c(532), s_c(532), t_c(1064), s_c(1064), S_a (532), S_a (1064), S_c(532), S_c(1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Okayama	532 nm w/polarization lidar	0.1-15 km	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Sapporo	532 nm w/polarization, 1064 nm lidar	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Sri Samrong	532 nm w/polarization, 1064 nm lidar	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Suwon	532 nm w/polarization, 1064 nm lidar	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Tokyo	355nm, 532 nm w/polarization, 1064 nm, 387, 408, 607 nm Raman lidar, sun photometer	0.1-15 km (7.5 m)	5-10 min.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), t_c(532), s_c(532), t_c(1064), s_c(1064), S_a (532), S_a (1064), S_c(532), S_c(1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Toyama	532 nm w/polarization, 1064 nm lidar	0.1-18 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, b'(R, 532nm)_‖/b'(R, 532nm)
Tsukuba	532 nm w/polarization, 1064 nm lidar, 523 nm HSRL	0.1-15 km (6 m)	15 mins.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), t_c(532), s_c(532), t_c(1064), s_c(1064), S_a (532), S_a (1064), S_c(532), S_c(1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥

3.3 Atmospheric Radiation Measurement (ARM)

http://www.arm.gov/

The Atmospheric Radiation Measurement (ARM) Program is a multi-laboratory, interagency program that was created in 1989 with funding from the U.S. Department of Energy (DOE). The ARM Program is part of DOE's effort to resolve scientific uncertainties about global climate change with a specific focus on improving the performance of general circulation models (GCMs) used for climate research and prediction. These improved models will help scientists better understand the influences of human activities on the earth's climate. In pursuit of its goal, the ARM Program establishes and operates field research sites, called Cloud and Radiation Testbeds (CARTs), in several climatically significant locations. Scientists collect and analyze data obtained over extended periods of time from large arrays of instruments to study the effects and interactions of sunlight, radiant energy, and clouds on temperatures, weather, and climate. Sites include instruments to measure atmospheric profiles of aerosols and cloud optical properties, surface eddy flux, and surface meteorology. The instruments available for CALIPSO validation are discussed below and in Table 3.

The following measurements from the ARM sites would be suitable for CALIPSO validation and are summarized in Table 3 (validated parameters in parentheses):

Southern Great Plains (SGP) Central Facility (aerosol height/thickness, cloud height/thickness, t_a(532nm), t_a(1064nm), s_a(532), S_a(532), t_c(532 nm), s_c(532), S_c(532), b'(R, 532nm)_‖/b'(R, 532nm)_^, ice particle size, ice cloud effective emissivity)

Sunphotometer measurements at 1020 and 499 nm

Multi-filter rotating shadowband radiometer at 500 nm

Raman Lidar (runs day/night with 39 m range resolution) with 355 nm depolarization channel and a 387 nm Raman channel

Ceilometer measurements at 905 nm

Micro-pulse lidar at 523 nm

mm-Wavelength cloud radar

The following instruments are also present but do not directly validate any CALIPSO parameters: condensation nuclei counter, optical particle counter (31 channels between 0.1-10 mm and one greater than 10 mm), ozone monitor, microwave radiometer (31.4 GHz), atmospheric emitted radiance interferometer (3-20 mm or 500-3300 cm^-1, resolution 1 cm^-1), radiosondes, 50 and 915 MHz Radar wind profiler/RASS, camera centered on zenith, whole sky imager (450 and 650 nm), narrow field of view sensor (869 nm, centered on zenith), absolute solar transmittance interferometer (1-5 mm or 2000-10000 cm^-1, resolution 2 cm^-1, pyranometer, pyrgeometer, pyrheliometer, uv-b radiometer, solar radiance transmission interferometer (620-1350, 1500-2050, 2020-2550, 2420-3080, 3010-3830, 4020-4300 cm^-1, 3 times a day), shortwave spectrometer, uv spectroradiometer, surface meteorological observing system (1 minute wind speed and direction, temperature, relative humidity, pressure, rain amount), temperature and humidity at 25 and 60 m, and a chilled mirror.

Southern Great Plains (SGP) Extended Facilities (sites listed in Section 7.1) (t_a(532nm))

Multi-filter rotating shadowband radiometer for 500 nm

Also, a surface meteorological observing system (1 minute wind speed and direction, temperature, relative humidity, pressure, rain amount) is present.

Tropical Western Pacific (TWP) - Manus Island, Nauru Island, and Darwin (aerosol height/thickness, cloud height/thickness,t_a(532nm), t_a(1064nm), s_a(532), S_a(532), ice particle size, ice cloud effective emissivity)

Ceilometer at 905 nm

Micropulse lidar at 523 nm

mm-Wavelength cloud radar

Sunphotometer at 1020 and 499 nm

Multi-filter rotating shadowband radiometer at 500 nm

The following instruments are also present but do not directly validate any CALIPSO parameters: microwave radiometer (31.4 GHz), atmospheric emitted radiance interferometer (3-20 mm or 500-3300 cm^-1, resolution 1 cm^-1), radiosondes, 915 MHz Radar wind profiler/RASS, whole sky imager (450 and 650 nm), absolute solar transmittance interferometer (1-5 mm or 2000-10000 cm^-1, resolution 2 cm^-1), pyranometer, pyrgeometer, pyrheliometer, uv-b radiometer, solar radiance transmission interferometer (620-1350, 1500-2050, 2020-2550, 2420-3080, 3010-3830, 4020-4300 cm^-1, 3 times a day), surface meteorological observing system (1 minute wind speed and direction, temperature, relative humidity, pressure, rain rate).

North Slope of Alaska - Barrow (aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥, ice particle size, ice cloud effective emissivity)

High spectral resolution lidar (HSRL) (100 m to 37.5 km with day/night operation) 532

nm w/depolarization and 1064 nm

Ceilometer at 905 nm

Micropulse lidar at 523 nm

mm-Wavelength cloud radar

Sunphotometer for 1020 and 499 nm

Multi-filter rotating shadowband radiometer for 500 nm

The following instruments are also present but do not directly validate any CALIPSO parameters: microwave radiometer (31.4 GHz), atmospheric emitted radiance interferometer (3-20 mm or 500-3300 cm^-1, resolution 1 cm^-1), radiosondes, 915 MHz Radar wind profiler/RASS, whole sky imager (450 and 650 nm), absolute solar transmittance interferometer (1-5 mm or 2000-10000 cm^-1, resolution 2 cm^-1), pyranometer, pyrgeometer, pyrheliometer, uv-b radiometer, solar radiance transmission interferometer (620-1350, 1500-2050, 2020-2550, 2420-3080, 3010-3830, 4020-4300 cm^-1, 3 times a day), wind speed and direction, temperature, relative humidity at 2, 10, 20, and 40 m and pressure, visibility, and precipitation at the ground.

North Slope of Alaska - Atqasuk (t_a(532nm))

Multi-filter rotating shadowband radiometer for 500 nm

Table 3: Summary of instruments describe above at the various ARM sites.

	Southern Great Plains Central Facility	Southern Great Plains Extended Facilities	Tropical Western Pacific	North Slope of Alaska (Barrow)	North Slope of Alaska (Atqasuk)
Sun Photometer	1020 and 499 nm		1020 and 499 nm	1020 and 499 nm
MFRSR	500 nm	500 nm	500 nm	500 nm	500 nm
Raman Lidar	355 nm with polarization and 387 nm, both with 39 m vertical resolution
Ceilometer	905 nm		905 nm	905 nm
Micro-pulse Lidar	523 nm		523 nm	523 nm
HSRL				532 nm with polarization, 1064 nm, both with 100 m vertical resolution and range to 37.5 km
Mm wavelength cloud radar	Yes	No	Yes	Yes	No
Other instruments not directly related to validation	Yes (see text)	Yes (see text)	Yes (see text)	Yes (see text)	No

3.4 Baseline Surface Radiation Network (BSRN)

http://bsrn.ethz.ch/

BSRN is a project of the World Climate Research Programme (WCRP) aimed at detecting important changes in the earth's radiation field, which may cause climate changes. The objective of the BSRN is to provide, using a high sampling rate, observations of the best possible quality, for short and longwave surface radiation fluxes. These readings are taken from a small number of selected stations, in contrasting climatic zones, together with collocated surface and upper air meteorological data and other supporting observations.

The following measurements from the BSRN sites listed in Section 7.1 would be suitable for CALIPSO validation (validated parameters in parentheses):

Sunphotometer (t_a (532 nm), t_a(1064 nm))

Also all stations measure global, direct, and diffuse broadband solar radiation while most stations measure downward longwave, temperature, relative humidity, and pressure. Payerne, Von Neumayer, and Boulder measure upward shortwave and longwave irradiance and have radiosondes. Toravere and Tateno measure upward shortwave and longwave irradiance.

3.5 Climate Monitoring and Diagnostics Laboratory (CMDL)

http://www.cmdl.noaa.gov/aerosol/

The CMDL of the National Oceanic and Atmospheric Administration (NOAA) conducts research related to the atmospheric constituents that are capable of forcing change in the climate of the earth or may deplete the ozone layer. Aerosol measurements began at the CMDL baseline observatories in the mid-1970s as part of the Geophysical Monitoring for Climate Change. The goal of this regional-scale monitoring program is to characterize means, variability, and trends of climate-forcing properties of different types of aerosols, and to understand the factors that control these properties.

The following measurements would be suitable for CALIPSO validation (validated parameters in parentheses):

Lidars at Mauna Loa Observatory and Boulder, Colorado are capable of measuring stratospheric and tropospheric aerosols and the height and thickness of cirrus clouds. A third lidar station at American Samoa will be operating. The lidars are restricted to nighttime measurements at 532 nm. The Mauna Loa Observatory lidar also measures 1064 nm aerosol scattering and water vapor in the troposphere using the Raman method. The lidars are permanently deployed and operated routinely. (Aerosol Height/Thickness, Cloud Height/Thickness)

3.6 Commonwealth of Independent States Lidar Network (CIS-LiNet)

http://www.cis-linet.basnet.by/

CIS-LiNet (Commonwealth of Independent States Lidar Net) includes stationary and mobile lidar stations all over former USSR countries. CIS-LiNet was established in 2004 in the frame of the International Science and Technology Center (ISTC) Project. The net’s aims are regular measurements of aerosol and ozone vertical profiles to study their large-scale spatial and temporal transformations.

Table 4 presents a list of instruments, the resolution in time and space of any available lidar, and the CALIPSO Level II parameters validated for each site in the network.

Table 4: List of instruments, vertical range and resolution, time resolution, and parameters validated for each station within the CIS-LiNet.

Station	Instrument	Lidar range (resolution)	Lidar time resolution	Validated parameter
Minsk	Backscatter Lidar 1064, 532, 355 nm w/polarization, CIMEL sunphotometer	2-30 km(64 m)	10 min	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Moscow	Backscatter Lidar 532 nm			aerosol height/thickness, cloud height/thickness
Sergut	Backscatter Lidar 532 nm	0.5-30 km (15-300 m)	10-30 min	aerosol height/thickness, cloud height/thickness
Teplokluchenka, Kyrgyzstan	Raman Lidar 532, 608 nm	2-20 km(37 m)		aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_c(532), s_c(532), S_a (532), S_c(532)
Tomsk, stationary	Raman Lidar 308, 532 nm, Backscatter Lidar 532 and 1064 nm, humidity, temperature, Aerosol Station, Standard Meteorological measurements, CIMEL sunphotometer	Raman: 8-50 km(60 m) Backscatter Lidar: 5-30 km (50-500 m)	Raman: 15 mins. Backscatter Lidar: 10-60 mins.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), S_a (532), s_a(1064), S_a (1064)
Tomsk, mobile	Raman Lidar 532 w/polarization, 608 nm	0,2-12 km (5-15 m)	1-12 min.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_c(532), s_c(532), S_a (532), S_c(532), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Vladivostok, stationary	Backscatter Lidar 532 nm	2-20 km (60 m)	10-30 mins.	aerosol height/thickness, cloud height/thickness
Vladivostok, mobile shipboard	Backscatter Lidar 532 nm	1.5-15 km(60 m)	10-30 min	aerosol height/thickness, cloud height/thickness
Yakutsk	Backscatter Lidar 532 nm	3-50 km (30 m)	15-60 min	aerosol height/thickness, cloud height/thickness

3.7 EARLINET

http://www.earlinet.org/

EARLINET’s objective is to establish a quantitative comprehensive statistical database of the horizontal, vertical, and temporal distribution of aerosols on a continental scale. The goal is to provide aerosol data with unbiased sampling, for important selected processes, and air-mass history, together with comprehensive analyses of these data. The objectives will be reached by implementing a network of 21 stations distributed over most of Europe, using advanced quantitative laser remote sensing to directly measure the vertical distribution of aerosols, supported by a suite of more conventional observations. Special care will be taken to assure data quality, including intercomparisons at instrument and evaluation levels.

Table 5 presents a list of instruments, the resolution in time and space of any available lidar, and the CALIPSO Level II parameters validated for each site in the network.

Table 5: List of instruments, vertical range and resolution, time resolution, and parameters validated for each station within the EARLINET.

Station	Instrument	Lidar range (resolution)	Lidar time resolution	Data products available for validation
Athens_EARLINET	355, 532, 387 nm lidar, meteorological data (P,T,U)	0.5-12 km (15 m)	6 mins. extinction only at night-time	aerosol height/thickness, cloud height/thickness t_a(532), s_a(532), S_a (532), t_c(532), s_c(532), S_c (532), ice cloud effective emissivity
Barcelona_EARLINET	532,607, 1064 nm lidar, aerosol spectrometer, pyranometer, sunphotometer	0.25-10 km (7.5 m)	1 min	aerosol height/thickness, cloud height/thickness t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064)
Bilthoven_EARLINET	355 nm and 532 nm Raman lidar and 1064 nm backscatter lidar	1-15 km (7.5 m)	30 min.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064)
Bucharest_EARLINET	532 nm, 1064 nm (scanning capability) Radiosonde, Meteo station (P,T,RH,winds)	300-12000m(6 m)	1 min	aerosol height/thickness, cloud height/thickness
Cabaw_EARLINET	355, 532 w/depolarization, 1064 nm Raman lidar, AERONET sunphotometer, Ceilometer, Radiosonde,10, 35, 95 GHz radar, and other instrumentation available (similar to ARM SGP site)	1-5 km	5 min.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064), b’(R, 355nm)_‖/b’(R, 355nm)_⊥, ice particle size, ice cloud effective emissivity
Garmisch_EARLINET	355 nm, 532 nm, 1064 nm lidar (HSRL), visibility meter, pyranometer, spectrally resolved UV 532 nm backscatter lidar	0.2-10 km (3.75 m) 1.5-40 km (15 m/3.75 m)	10 s-3 min extinction 532 at daytime 1-7 min	aerosol height/thickness, cloud height/thickness t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064)
Hamburg_EARLINET	355, 387, 407, 532, 607, 1064 nm Raman lidar, 355, 532nm pure rotational Raman lidar, 1064 s+p-pol, and AERONET sunphotometer, ceilometer	0.3-10 km (15 m)	10 s	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064), b’(R, 355nm)_‖/b’(R, 355nm)_⊥
Jungfraujoch_EARLINET	355, 387, 532, 607, 1064 nm w/polarization (355 nm); Raman lidars- Pure rotational Raman at 532 nm for temperature aerosol extinction/ backscatter measurement, sunphotometer (Meteoswiss),	4-11 km (7.5-300m m)	100 s	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064), b’(R, 355nm)_‖/b’(R, 355nm)_⊥
L’Aquila_EARLINET	351nm, 382 nm, 393nm, 403nm Raman lidar, PTU and PTO₃ radiosonde	.3-8 km a.g.l. (30 m)	10 mins.	aerosol height/thickness, cloud height/thickness, ice cloud effective emissivity
Lecce_EARLINET	351, 383 w/ depolarization, 404 nm Raman lidar, AERONET sunphotometer, meteo station (P, T, RH, wind), Vaisala radio sonde for (P,T,RH)	0.4 - 7 km (1.5 m)	3 mins. extinction, depolarization, water vapor, and temperature profiles at night-time only	aerosol height/thickness, cloud height/thickness, t_a(532), t_a(1064), b'(R, 351nm)_‖/b'(R, 351nm)_⊥
Leipzig_EARLINET	355, 532 (polarization), 1064, 387, 408, 529, 530.2, 533.7, 535, and 607 nm Raman lidar, sun photometer (380, 440, 500, 670, 870, 1020, and 1640 nm), Vaisala radio sonde (P, T, RH)	0.5 km - trop. for extinction and 0.1 - trop. for backscatter (60 m)	30 mins. (raw 30 s)	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064), b’(R, 355nm)_‖/b’(R, 355nm)_⊥, ice cloud effective emissivity
Minsk_EARLINET	355, 532, 1064 nm and 532 w/polarization lidars; AERONET sunphotometer	Lidar #1 (lidar #2) 0.3(1)-10(30) km (15 m (128m))	5 (30) mins.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), b'(R, 532nm)_‖/b'(R, 532nm)_⊥
Munich_EARLINET	355, 387, 532, 607, 1064 nm lidar	0.2-5 km (3.75 m)	0.1 s	aerosol height/thickness, cloud height/thickness t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064)
Napoli_EARLINET	355, 387, 407, 532, 607 nm, Raman lidar, meteo. station (P,T,RH)	0.25-12 km (15 m), 0.1-8 Km (60m) for WV mixing ratio	1 min.	aerosol height/thickness, cloud height/thickness, t_a(532), s_a(532), t_a(1064), s_a(1064), S_a (532), S_a (1064), t_c(532), s_c(532), S_c (532), t_c(1064), s_c(1064), S_c (1064),
Neuchatel_EARLINET