Joint RSMAS-CEOS Infrared Validation Workshop
March 5-6, 1998


Rosenstiel School of Marine and Atmospheric Science
University of Miami
Florida, USA

March 5, 1998

The workshop was chaired by Ian Barton (CSIRO). Participants included Otis Brown (RSMAS), Peter Minnett (RSMAS), Walt McKeown (NRL), Craig Donlon(CCAR, University of Colorado), Jennifer Hanafin (RSMAS), Goska Szczodrak (UBC, Vancouver), Andy Jessup (APL, University of Washington), Gary Wick (University of Colorado), Andy Harris (UK Met Office), E. Theocharous (NPL), Fred Prata (CSIRO), Tim Nightingale (Rutherford Appleton Lab), Tom Sheasby (University of Leicester), Jim Butler (NASA/GSFC), Bob Evans (RSMAS), Frank Palluconi (JPL), Carol Johnson (NIST) and Bob Kannenberg (NASA/GSFC).

1.0 Introduction

Barton welcomed participants and announced that this workshop is intended to be a forum in which the various groups involved in the validation of satellite measurements of surface temperatures can discuss sharing data and participating in one another's field activities. He encouraged participants to look beyond their respective areas of expertise when considering inter-comparison activities (i.e., how can the validation community most effectively work together as a whole?).

2.0 Objectives and Outputs

Barton cited the following objectives and outputs for the workshop:
  1. Establish a mechanism where sea surface temperature (SST) and land surface temperature (LST) validation plans of each agency are available to other agencies. Currently official plans for MODIS and other instruments are in various stages of development and many are available on the Web. There are other CEOS agencies with plans, and we need to look at strengthening the links between the various agencies, plans, etc.

  2. Recognize that, for each new instrument, no single agency has all the necessary facilities available for validation.

  3. Develop measurement and data exchange protocols to maximize benefits.

  4. Devise a strategy for ensuring that the exchange of satellite and ground data for validation purposes occurs, so that each agency can benefit from the validation campaigns of other agencies. This may be done through CEOS working groups, or through separate agreements or MOUs with each agency (some already exist, like between NASA and NASDA).

  5. Produce a document or establish a Web page describing the validation instruments, Points-of-Contact, planned cruises, etc. Establish guidelines about a period of exclusive use of campaign data.

  6. Produce a document containing the essential information about future satellite radiometers and how to ensure getting access to their data. This may be done using existing CEOS facilities.

  7. Publication of a meeting report to ensure that our deliberations and decisions are available to a wider audience.

3.0 SST Validation Plans

3.1 Advanced Along Track Scanning Radiometer (AATSR)

3.1.1 Instrument Overview

Nightingale reported that the AATSR instrument, the third in the ATSR series, is to be a payload instrument on ESA's ENVISAT-1 polar-orbiting mission (scheduled for launch in 1999). AATSR has the same signal channels and embodies exactly the same viewing principle as ATSR-2 (i.e., thermal channels at 3.7, 10.8, and 12 microns wavelength, and reflected visible/near infrared channels at 0.555, 0.659, 0.865, and 1.61 microns wavelength). The main objective of AATSR is to contribute to the long-term climate record of global SST by extending the current ATSR-1 and -2 global data sets well into the next decade. This could eventually provide the climate research community with uniformly high-quality global SST data over a period of 12-15 years (depending on the lifetime of AATSR).

Like its predecessors, ATSR-1 and ATSR-2, AATSR will carry on-board calibration systems for the thermal channels, using two black bodies viewed every scan and, for the visible channels, a sample of solar radiation scattered from a diffuser plate is viewed once per orbit. Unlike ATSR-2, it maintains full digitization of all channels all the time and has no limited-data-rate operating modes.

Nightingale stated that requests for AATSR data must be made through ESA. McKeown asked what AATSR's approximate SST accuracy will be, and Nightingale replied that it will be 0.3K.

3.1.2 ESA AATSR Validation Plan

Sheasby provided an overview of the AATSR Validation Plan, including principles of validation, establishment of a measurement protocol, implementation of validation activities, details of planned campaigns, and post-campaign analysis. The plan is available online here Sheasby and Donlon encouraged workshop participants to access the document, which is still evolving, and submit comments or suggestions.

The group debated the merits of providing raw data to the validation community at large. Brown cited the example of brightness temperatures, where the original counts are also provided. Later on down the line somebody may come up with a better way to compute the brightness temperatures from the counts so, from that standpoint, it makes sense to provide the counts as well.

Barton asked that AATSR and other instruments publish detailed validation campaign plans on the Web, to facilitate inter-comparison of data; most instruments currently have some kind of plan available. Brown added that the information should include not only where and when campaigns will be held, but what kinds of products and measurements will be involved, and how can these be obtained An exchange needs to be mediated somewhere as to how data changes hands, and CEOS is probably the right place to begin this discussion. Brown stressed that the IR community needs to look at long-term cross-comparison and cross-validation plans so as to have consistent data sets for use by future environmental scientists.

Harris should contact Evans to discuss match-up databases for AVHRR and ATSR data, and how these might apply to AATSR data (Action Item 1).

3.2 NASA MODIS Validation Plan

Minnett reported that the MODIS IR SST Validation Plan is available online at: http://www.rsmas.miami.edu/modis

Minnett pointed out that MODIS includes both land and atmosphere components, and the MODIS Ocean group will be collaborating with the Atmosphere group (ER-2 flights, etc.) as well as other instrument teams. The MODIS SST Validation Plan is really a validation of the atmospheric correction. The plan calls for comparison of "like with like" (i.e., IR radiometry from ships and aircraft). Measurements will be taken with the Marine-Atmosphere Emitted Radiance Interferometer (M-AERI), band-pass radiometers, and conventional in situ sensors (buoys). Issues for analysis include regional and seasonal effects, the skin effect, and diurnal heating.

Minnett listed the objectives of MODIS field programs as follows: use M-AERI; take ancillary measurements in the atmosphere and ocean; make measurements in varied regions; study ocean thermal skin effects; improve robustness of SST retrieval (e.g., variations in water vapor and aerosols); and validate SST retrievals.

Minnett reviewed a list of M-AERI cruises completed over the last couple of years. Upcoming M-AERI cruises include a voyage from Seattle to either New Zealand or Tasmania in Fall 1998. Collaboration with a Japanese ship is being explored, as is a collaboration with an Indian ship in the Arabian Sea (where there is heavy aerosol contamination). M-AERI may also be deployed on fixed platforms; possibilities include the Chesapeake Bay light tower (part of CERES), US Navy towers in Florida Bay, the North Sea research platforms (a Dutch site), the Mediterranean Sea research platforms and platforms located in western Australia. Minnett cited cleanliness of environment and safety of the platform sites as important selection criteria.

Minnett indicated that the results of the previous three-day instrument intercomparison will help to determine the type of band-pass radiometer selected by MODIS to supplement M-AERI measurements. Theocharous pointed out that there are many more radiometers commercially available than those compared at the workshop. He will send a list of radiometers to Minnett for publication on the Web (Action Item 2). Barton will ask Johnson if NIST has a list of available radiometers and, if so, request that she supply it to Minnett for publication (Action Item 3).

3.3 Sea State Measurement

Donlon noted that so far discussion has not touched on a sea state measurement. Currently this is a very subjective measurement, perhaps taking the form of a half-hourly visual report from a ship's bridge. Minnett agreed that sea state is a very difficult thing to quantify. He has attempted to make sea state measurements using panoramic views from a camera. McKeown stated that an NRL scientist has developed an algorithm to calculate sea state in the visible range--perhaps this can be modified and applied to IR?

3.4 NASDA Global Imager (GLI) Validation Plans

Barton briefly discussed GLI validation plans, as NASDA representatives were unable to attend the workshop. GLI is very similar to MODIS in both design and validation strategy, and there has been a good deal of synergy between the two instrument teams. GLI validation activities will be conducted from test sites in the Bering Sea and the Japan Sea, as well as coastal sites in Japan. The Japanese fishing industry has so far provided strong support for validation activities. Bulk SST (BSST) and skin SST (SSST) measurements are among the highest priorities for GLI validation.

At this time the GLI land validation plan is not as well developed as the ocean validation plan. Each PI will be expected to provide ground data to validate their particular algorithm.

3.5 CSIRO Validation Plans

Barton indicated that CSIRO is working with MODIS, AATSR and GLI. CSIRO has placed instruments aboard commercial ferry boats (Townsville and Perth) in order to collect daily data over a fixed area. CSIRO also plans to place instruments aboard ships of opportunity operating in Australian waters. Barton presented examples of ATSR and AVHRR data, looking at the skin/bulk temperature difference. In situ data taken by CSIRO (using both a radiometer and a thermosalinograph) compared well with the satellite data. Barton noted that so far modellers have relied primarily on BSST measurements, but the true SST picture is much more complex than that, and requires an algorithm that factors in the SSST.

4.0 LST Validation Plans

4.1 CSIRO Validation Plans

4.1.1 IR

Prata stated that he has been asked to derive IR LST algorithms for both AATSR and GLI. The LST algorithm will be a regression-based algorithm that will factor in 16 types of existing land classifications, thus bypassing the surface emissivity problem. (Prata will not derive a snow or ice algorithm.) He explained that LST is not really a skin temperature, as radiation is being emitted from a variety of sources (deep within the canopy, leaves, ground, etc.). There are also angular effects to consider. Analysis of ATSR-2 data shows that there can be significant variations in emissivity depending on viewing angle. Prata presented some ATSR images taken over Australian validation sites.

4.1.2 Visible

Prata presented visible LST data collected in April 1997 during a collaborative effort between CSIRO and the University of Nottingham. The purpose of this activity was to validate ATSR-2 spectral radiance measurements. Overall ground measurements compared well with the ATSR-2 measurements.

4.2 NASA ASTER Validation Plans

Palluconi explained that the ASTER validation effort focuses on LST measurements; there are some Japanese scientists interested in coral reefs but, other than that, there is little interest in ocean measurements. ASTER will validate the radiance at sensor (Level 1), and then the surface leaving radiance (Level 2). ASTER consists of three separate instruments, or components: VNIR, SWIR and TIR. There will be no space-view calibration for ASTER. Jessup stated that he may be interested in obtaining some high-resolution ASTER data, and he will discuss this with Palluconi (Action Item 4). Primary ASTER validation sites are Lake Tahoe, Salton Sea, Railroad Valley and White River Valley. Barton suggested that ASTER could benefit greatly from collaborative validation efforts with MODIS. Prata noted that ASTER could use SST data to help validate its atmospheric correction measurements. Palluconi indicated that, 6 months after launch, anybody can request ASTER data, and he encouraged participants to do so. The ASTER Validation Plan is available online through the EOS Web site.

5.0 Radiometer Development

5.1 Ship of Opportunity Sea Surface Temperature Radiometer (SOSSTR)

5.1 .1 Background

Donlon asserted that there is presently a serious lack of geographically widespread and temporally dense in situ SSST measurements. This hinders the validation, long-term stability and interpretation of SSST satellite measurements. It also hinders the development of skin-to-bulk temperature transfer models. Donlon cited the high cost and limited availability of extremely accurate radiometers as another limiting factor for in situ SSST measurements.

5.2 SOSSTR Design

Donlon presented data gathered with Tasco THI-500L radiometers, which are inexpensive but require constant calibration. When compared at sea to the precisely calibrated sea surface temperature radiometer (SISTeR), the Tascos provided good data even without protection from the elements, although the data did not reach the desired 0.1°C accuracy . To improve the accuracy of the Tascos, Donlon has housed two of them within an enclosed (but not sealed) unit called the ship of opportunity sea surface temperature radiometer (SOSSTR). One radiometer looks at the sea, while one looks at the sky. SOSSTR also contains two black bodies, one ambient and one hot. Donlon believes that the SOSSTR units can be constructed for between 10 and 15 thousand dollars each, meaning that a large deployment would be relatively inexpensive. He concluded that we need long-term, ongoing baseline SSST measurements, and recommended that an in situ working group be formed to compare data and share knowledge. (For more information, refer to Donlon et al "Solid State Radiometer Measurements of Sea Surface Skin Temperature.")

5.3 Proposed University of Washington Applied Physics Lab (APL) Radiometer Design

Jessup reviewed his proposed radiometer design, which calls for enclosing the sensors and black bodies within a sealed, temperature-controlled housing. (The radiometers inside the unit would be Heimann KT-15 models.) The housing would be filled with dry nitrogen, and the sensors would look out through an IR-transparent window, equipped with a wiper and fluid reservoir to periodically clean salt, spray, etc. Harris pointed out that adding the window means that there is no true end-to-end calibration. Jessup acknowledged this, but said that if he can find an IR-transparent window that can be very accurately characterized, the protection it would afford the sensors could more than account for the added uncertainty introduced. He added that he may be over-engineering in response to the worst-case scenario (e.g., a huge wave hits the unit), and asked participants for their feedback. Barton stated that , in his opinion, the error introduced by the window may well eat up the .1°C accuracy. Donlon too felt that the window trade-off may not be beneficial. Both Barton and Donlon agreed, however, that the window is worth checking out so long as the design of the unit allows the window to be removed later. Jessup has begun investigating IR window materials (e.g., zinc selenide), and will look at testing windows and the effects of various cleaners.

5.4 JPL ASTER Radiometer

Palluconi explained that the ASTER unit contains an Everest 4000.4GL radiometer, housed within a very well-insulated box. The attempt to isolate the radiometer passively with the insulation appears to have caused temperatures to drift up significantly.

5.5 General Comments

Donlon advised that radiometer developers try to keep their units as lightweight as possible. Also, for most point-and-shoot radiometers, a look angle of less than 40: is desirable; otherwise, roll and pitch must be sampled very precisely. Jessup suggested that at the next inter-comparison workshop a surface disrupter and an imager be used for the measurements taken from the rooftop platform. Barton noted that originally the inter-comparison workshop was to include a couple days of ship measurements; perhaps this can be incorporated into the next workshop. Jessup indicated that for a future workshop instruments might be mounted on the FLIP platform, which is unique in that it orients itself with the wind and remains very stable. This platform would be safe and stable enough so that the NIST or APL black body could be used on-board. Barton stated that one of these two black bodies, plus an M-AERI, should be incorporated into future workshops and field activities whenever possible.

6.0 Surface Temperature Validation Web Site

Barton stated that there are avenues through CEOS with which workshop participants can establish protocols and frameworks to structure validation activities between groups. He suggested that surface temperature validation information (e.g., instrument data, upcoming field activities, etc.) be made available on the Web, and asked participants to think about whether this information should be kept within a single location by a Web master, or if it should be distributed among various sites and made available through links. The Web site will allow satellite operators access to ground validation data. Barton will investigate setting up a Web site with CEOS resources (Action Item 5). In the meantime, however, the results of the inter-comparison activities of March 2 - 5 can be published on the RSMAS Web site (Action Item 6).

7.0 Coordination of Campaigns and Cruises

7.1 CSIRO

Refer to paragraph 3.5.

7.2 NASA MODIS

Refer to paragraph 3.2.

7.3 University of Washington APL

Jessup reported that APL will participate in a NOAA cruise in the May and June of 1998. He hopes to have his prototype radiometer unit built by July 1998, and then conduct testing from the Hood Canal Bridge and the ferry in Puget Sound. Platform Harvest in 1999 may be another possible testing site. Jessup is also interested in taking measurements in the Gulf of Mexico in 1999, and this is the experiment for which he would like to obtain high-resolution ASTER data.

7.4 Other Possible Ships of Opportunity

Minnett suggested that Jessup may want to investigate putting a radiometer package aboard one of the ships that travels between Seattle and Yokohama. Minnett reported that he and others at RSMAS have been exploring the possibility of mounting radiometer packages aboard Caribbean cruise ships. Donlon added that these are the kinds of possibilities we need to explore to maximize the ship of opportunity strategy.

End of Day 1.

March 6, 1998

8.0 (Continuation of Section 5) Radiometer Development

8.1 RAL SISTeR Radiometer

Nightingale described the SISTeR (The Scanning Infrared Sea Surface Temperature Radiometer) Radiometer which is based on an ellipsoid mirror which allows a small foreoptics window. This alllows for smaller internal black body calibration targets and a narrow exit slit which protects against the elements. The radiometer's optical path is chopped at 100 Hz and the radiation is passed through one of six possible filters before arriving at a DLTGS detector. The chopper is close to the detector and the filter is between chopper and detector. Barton pointed out that the chopper could change temperature when the hot and cold BB is viewed (In Barton's radiometer the chopper is used to view a reference BB rather than relying on the temperature of the chopper and the calibration BBs are viewed by the pointing mirror and the chopper is high reflectivity (gold) coating. The chopper and filter wheel is between the parabolic primary and entrance aperture.). Harris suggested using a gold coating on the back of the chopper would improve the performance.

For sea surface temperature measurement including a sky scan the measurement cycle is about two minutes which includes a look at the two blackbodies. In situ calibration with CASOTS BB indicates no bias and a peak to peak noise of about 0.1°K (Note: The BBs are not temperature controlled so the heating is kept constant but their temperature changes.) In an example, crossing a boat wake near a buoy produced several degrees C change in the SST measurement and the mixing of the surface layer (thermocline) showed up in the buoy measurement at a 1 meter depth.

8.2 NRL Buoy Radiometer

McKeown stated that NRL were hoping to install infrared radiometers on some 300 buoys to observe the sea skin temperature. It was proposed to mount a system at 20-25 m with a rain shield, spray shield and a rotating (Tasco maybe) radiometer with a single calibration BB. A conical mirror above the radiometer is to be used to feed the radiometer and create a large footprint. A full sky radiometer will be used to obtain sky irradiance measurement. The buoy will collect data when it is vertical, i.e. reasonably calm conditions, and the system could be sealed off during rough conditions.

Harris suggested that 5 minutes of observations will allow a lot of water to pass by and this will allow looking at a reasonable area. The question of all sky irradiance measurements vs looking at the sky at the specular angle (also involved is direct vs diffuse reflectance) involved in the SST measurement. Donlon pointed out that SST often uses specular sky reflectance only whereas with a thermal imager the diffuse reflection from a cloud can be clearly seen so the diffuse component is relevant as well (although a small additional correction).

Minnett said Eppley will not make a narrow filter all sky radiometer because such a design is not seen as possible. He also said that rain will wash the salt contamination from exposed optics for mast mounted radiometers.

9.0 A Data-base for Measurements

The question of a data-base of measurements was discussed and Evans (RSMAS) offered to use the resources of Uni of Miami to help set up a WWW page to point to the sources of data themselves (especially for the large continuing data sets). Barton suggested that the National Space Agencies could be used to endorse the data base activity. Evans pointed out that some countries did not have a problem with individuals using data; however, where the interest was to provide data to the general community much more extensive negotiations (several years) may be required.

Barton suggested that there be a separation of data used for cal/val and that used for research in that cal/val data should be made widely available as soon as it is reduced and understood by the generator. Cal/Val data would be released quickly but if the same data was used for research CEOS could recommend the originators be contacted and informed that the data is to be used for research purposes.

Minnett suggested a 9 month submission period for data and after 12 months the data base administrator would release any data in the base to qualified users. Evans pointed out that where data sets are built from national measurement systems the real time or near real time data sets can have serious problems since they may have limited quality control.

10.0 Communications

10.1 Establishment of a WWW site

Barton suggested that a CEOS IR Cal/Val web page (CEOS WGCV WWW) could be used to provide a link to the data sets that are maintained by individuals or organizations. WWW pages could be established for instrumentation description, contacts, Campaigns (Land/Sea)(with protocol descriptions), meetings (CASOTS, Miami etc.), meta-data data sets.

Action items were placed on the following attendees to bring the WWW site together.

10.1.1 Barton to liaise with the CEOS WGCV to host the Ad-hoc IR Group WWW site. This would require a couple of paragraphs describing the interests of the Group and include links to (a) Campaigns, (b) Instruments, (c) Meetings, (d) Contacts list, and (e) Meta-data data-base.

10.1.2 Sheasby to establish a WWW page to include links to planned campaigns over both land and sea. The page would also provide information on measurement protocols etc. (initially through the AATSR validation Plan).

10.1.3 Donlon to establish an instrumentation page which would provide links to information on particular radiometers and other associated instrumentation.

10.1.4 Barton would also establish a page (possibly under the CEOS WGCV) to provide links to meeting reports. Initially these would consist of the CASOTs meetings and those currently being held in Miami.

10.1.5 Minnett agrred to start a contacts page based on the information collected for the current workshops.

10.1.6 Minnett also agreed to provide a meta data-base page which would provide links to data bases held by individual investigators.

The basic data sets are assumed to reside with the collecting individuals and organizations and in some cases the National Space Agencies. There was discussion of establishing mailing lists and using the list to alert cal/val to new items on web pages or meeting announcements etc. Using majordomo was suggested by Donlon but Barton suggested just establishing a list and letting people copy the list to send e-mail. The difference is majordomo requires a mail server and the other method is almost self-maintaining.

Barton indicated he would write up and circulate for comment the ideas which have been accepted at this workshop. The next CEOS cal/val meeting will be next July in Tokyo and he would report on this workshop at that meeting.

Evans indicated that Uni. of Miami would have all AVHRR and MODIS data and for cal/val purposes they would be willing to do the extractions to match the cal/val data. Barton indicated that the general agreement of the CEOS member agencies was that data for climate research including cal/val should be freely available. But, Barton said that it may be necessary to respond to the recent ENVISAT AO to insure timely delivery of data and data of the highest spatial resolution. The ENVISAT AO may contain money for the development of cal/val instrumentation. Barton asked if this group or a CEOS group should respond to this AO. It was said that this would move things to a new level of cooperation but would require someone to step up and lead the effort. Barton then suggested that the relevant USA institutes should put together a brief proposal which would be well received. Ian said the Japanese SST investigators are also likely to be forming a plan.

11.0 Closing Comments

11.1 Following meeting

It was agreed that a future meeting for both the radiometer-BB inter- comparison and the Validation Workshop would be extremely valuable. Sometime in the 1-2 years window would seem appropriate.

Barton mentioned that the Validation Workshop would have benefited form stronger agency representation particularly from NASDA, NASDA and ESA.

11.2 Minutes

Barton said he would provide minutes of the meeting and a set of recommendations. The draft minutes would be forwarded in the next two weeks for comments before final dissemination.

11.3 Thanks

Barton thanked Bob Kannenberg (NASA) and Frank Palluconi (JPL) who have provided extremely accurate and thorough minutes of the two-day meeting.

Barton also thanked Otis Brown and Peter Minnett and RSMAS, Uni of Miami for the local arrangements and support for the two Workshops.

12.0 Action Items

  1. Harris, Evans: Harris should contact Evans to discuss match-up databases for AVHRR data, and how these might apply to AATSR data.

  2. Theocharous: Send a list of radiometers available commercially, but not used at the intercomparison workshop, to Minnett for publication on the RSMAS Web site.

  3. Barton: Ask Johnson if NIST has a list of available radiometers and, if so, request that she supply it to Minnett for publication on the RSMAS Web site.

  4. Jessup, Palluconi: Jessup will contact Palluconi to discuss obtaining high resolution ASTER data for use during validation activities in the Gulf of Mexico in 1999.

  5. Barton: Investigate setting up a surface temperature validation Web site with CEOS resources (now superceded below).

  6. Minnett: Publish results of March 2 - 5 intercomparison workshop on the RSMAS Web site (now superceded below).

  7. WWW Action Items

    (10.1.1) Barton to liaise with the CEOS WGCV to host the Ad-hoc IR Group WWW site. This would require a couple of paragraphs decribing the interests of the Group and include links to (a) Campaigns, (b) Instruments, (c) Meetings, (d) Contacts list, and (e) Meta data-base.

    (10.1.2) Sheasby to establish a WWW page to include links to planned campaigns over both land and sea. The page would also ptovide information on measurement protocols etc. (initially through the AATSR validation Plan).

    (10.1.3) Donlon to establish an instrumentation page which would provide links to information on particular radiometers and other associated instrumentation.

    (10.1.4) Barton would also establish a page (possibly under the CEOS WGCV) to provide links to meeting reports. Initially these would consist of the CASOTS meetings and those currently being held in Miami.

    (10.1.5) Minnett agreed to start a contacts page based on the information collected for the current workshops.

    (10.1.6) Minnett also agreed to provide a meta data-base page which would provide links to data bases held by individual investigators.

  8. Barton to formulate a set of recommendations to take to the next CEOS WGCV meeting in Tokyo during July 1998. Also, to report on the inter-comparison and validation workshop at the Tokyo meeting.

  9. Barton to provide a draft set of meeting minutes prior to the release of a final set which would be made available through the WWW.

RECOMMENDATION TO CEOS PLENARY FROM THE WGCV

The thermal infrared validation community have met in Miami during March 1998 for a round-robin instrument inter-comparison and a satellite validation workshop. The meeting agreed to foster close international collaboration in the collection and analysis of ground truth data for the validation of geophysical products derived from thermal infrared satellite data.

To ensure that validation data sets are available to the satellite operators in a timely manner it is recommended that the appropriate satellite data be made available to the ground data providers in near real-time and free of any charges. In return the ground data collectors will provide validation data sets to the satellite community in a timely manner. It is also recommended that both the ground data supplied by the data collectors and the associated satellite data are only initially available for use in satellite instrument calibration and data product validation and should not be used in any other manner unless agreed by the data producer.